why did the sino-soviet split have to happen?

This is especially silly if you consider that the USSR was helping other countries fight against colonialism, while the PRC both helped the premier imperialist force in the world to win in Afghanistan, and engaged in what could be argued to be imperialism against Vietnam.

By that logic, the USSR should have nuked the PRC the moment it took action against Vietnam to 'play both sides' and to fight against PRC's imperialism/'imperialism'.

It’s not “me” who’s saying this. This is just standard Chinese narrative on why the PRC sided with the US to destroy the USSR

So, you uncritically believe the PRC on why destroying its allies was good, and choose to regurgitate that narrative when it's obviously ass?

You also need to understand that Sino-Soviet relationship had always been tense

Not exactly a reason to actively help NATO take down your allies and make NATO's positions in the world stronger.

It wasn’t just the Russian Empire getting involved in the Eight-Nation Alliances to carve out the Qing Empire and annexed the Northeast, but also when Stalin insisted on the independence of outer Mongolia to assert its influence in Central Asia, his insistent on using Port Arthur (Lushunkou) as “shared” Sino-Soviet naval base (i.e. stationing Soviet troops in Chinese province), retaining the control of Chinese Eastern Railway, and the refusal to return Vladivostok (Haishenwei) to Chinese sovereignty.

Sure. And you claim that this is a good reason to destroy your major ally and shoot yourself in the foot?
Also, you talk about realpolitik, and now you bring up past offences when realpolitik in large part revolves around ignoring grudges. You are clearly not thinking about this in any sort of rigorous manner, but are just trying to invent a way to present the relevant actions of the PRC as somehow good.

Some of these major issues got settled after the Mao-Stalin meeting in 1949-50 during the “honeymoon” period but the threat of “Soviet imperialism” has always been latent

By your logic, the USSR should have destroyed the Chinese communists during the civil war and handed China over to anti-communists. That would have been a very swell move for both the USSR and the workers of the world, wouldn't it?

After Stalin died, the Soviets went mask off with their intentions and started to threaten Chinese national sovereignty

'Went mask-off'? You mean the state that was assisting multiple national liberation movements in the world in Asia, Africa, and the Americas at the time was 'going mask off'?
You also have not presented any sort of evidence for the USSR seriously threatening the PRC's sovereignty.
Also, are we to believe that NATO did not threaten the PRC's sovereignty?

It’s a lot more nuanced than people are making it out to be

You are not doing a good job of presenting this supposed nuance, and have already contradicted your claim that 'this is just realpolitik' when you brought up then-past offences of the USSR and, even less relevantly, of the Russian Empire (and forgot to bring up the offences of the western powers like the British Empire, including the fact that they were and are actually trying to threaten the PRC's sovereignty).

Just because the PRC and the Soviet Union share the same ideology doesn't mean they are above geopolitics.

But it does??? What the fuck is class solidarity meant to mean otherwise, it was and is in the best collective interest of the working class for socialist countries to support each other

the ignorance of the terrible impacts which hampered development which followed the loss of Soviet industrial aid and the capital to modernize (and not have to have peasants smelt pig iron in their backyards), and loss of advisors for proper, efficient, safe productive practice and managing contradictions with wrecking and between the new proletarian manager and worker relationships that the soviets went through and had valuable lessons in, and countless other things is astounding. Defending China doing shit like funding muhajideen terrorist groups and child-r*ping warlords alongside the largest most violent capitalist empire in history in the US to attack the Soviets and and helping make the suffering of Afghanistan what it became and is to this day is grotesque and unhinged, almost as Deranged as post split chinese foreign policy. And is TRIPLY ignorant because China has had to face its own blowback FOR EXACTLY THAT, due to them hosting and financing CIA/ISI terrorist training camps in Pakistan on the border of Xinjiang.

You're making incoherent gestures based on abstract images youve imagined

But it didn't hurt China in the long run

TIL that destroying your allies and making your alliance less capable of effecting change in the world doesn't hurt you.

Or are you going to claim that the PRC+Russia today are more capable of fighting off NATO? When NATO is now capable of openly and to the loud support of its people carrying out invasions, genocides, and coups with nobody to stop them doesn't hurt the PRC?

I do hope that the PRC comes out on top in its struggle with the US, but claiming that the PRC+Russia can better withstand NATO's harassment than the PRC+the USSR is very silly.

China was able to procure tech from the West

While also making itself quite dependent on the West and opening itself to having its exports and imports cut off, and while also diminishing the rights of its workers (albeit, this latter point has to do with the liberalisation of the economy, and not, strictly speaking, with the silly activities to destroy its own allies and potential allies).
Thankfully, the PRC seemingly did manage to overcome being gradually cut off from western technologies, but the PRC also does seem to keep surrendering ground to NATO, such as allowing its banks to submit to the demands of NATO.

and more or less steal the West's manufacturing capabilities thanks to the short-sightedness of Western capitalist who didn't look part cost savings from labor arbitrage

Notably, neither this point nor the previous required the PRC to actively help NATO in Afghanistan or to invade Vietnam.

I don't have time to deal with the entire rest of the comment right this moment.

EDIT:

And the funny thing is China used the same exact playbook the late Ming did to bridge the tech gap: they gesture towards embracing whatever popular ideology and governance is in vogue at the West if you would only give us the tech

And that's kind of a silly strategy to employ against the opponent that betrays its own allies, and that can and does very easily smear its enemy-states that employ the same systems of governance and the like anyway.
Also, a lot of people do seem to not understand that there is a significant difference for the working class between living under a planned economy and one with a significant degree of privatisation. I am not sure if you are one such person, but I am getting the expression that that is a likely case.

But unlike the West, China rarely makes the same mistake twice. The problem with the late Ming/early Qing was that the West would eventually figure out the ruse, and imperial China lacked the means of being truly innovative after the tech transfer was cut off. This was not so with the PRC.

So, you are just going to leave it at that, with no basis provided for how that is not the case with the PRC that NATO would figure out the 'ruse' (actually just playing the capitalism game and making yourself a source of cheap labour and resources for NATO on conditions that make you extremely competitive compared to the other neo-colonies and using that advantage to get ahead in the hopes that the West would not react fast enough - I do not see how there is any 'ruse' involved). This is especially silly, considering that NATO has been increasing its anti-PRC effort.

Just because the PRC and the Soviet Union share the same ideology doesn't mean they are above geopolitics

Which is irrelevant to the topic, unless you want to argue that it's in the PRC's interest to ally with NATO and then be crushed by them after it has no strong allies left instead of siding with states that have ideologies similar to yours and which have proven themselves willing and able to fight against colonialism and help others do so as well.

Geopolitical alliances are ever-shifting

And the point here is that this shift was bad for the communist and anti-colonial movements at large, and cost the PRC its allies. I argue that it was ill-conceived, and am not seeing any good arguments in favour of this shift.

The Sino-Soviet split officially ended with Gorbachev's visit to Beijing, so it lasted only a couple of decades

So, it only ended when the socdem who admitted to wanting to destroy the USSR took over the USSR, privatised the economy, and sought friendship with colonial metropoles instead of their dominions. Just swell.

And now Russia is closer to China than ever even when they don't even share the same ideology

Now Russia is garbage and will need to be handled if and when NATO is gone.
Russia is now a semi-peripheral state - it is on the colonial periphery of NATO (and very likely now also of the PRC, but I have not studied the economic relations between Russia and the PRC enough) while also having its own periphery (in the form of some of the former parts of the USSR, such as Ukraine). It is both much weaker than the USSR and also not only isn't interested in the world's anti-colonial struggle beyond opposing NATO and, maybe, elevating itself from the semi-peripheral status, it is directly interested in simply becoming a metropole.

Why you are praising the PRC for being close with obviously shitty capitalist states and also for distancing from and sabotaging communist-led ones is beyond me.

As another example for why geopolitics have little to do with ideology, just look at how almost all Sunni Arab countries have betrayed the Sunni Arab Palestinians to the Zionists while the Sunni Arab Palestinians' greatest saviors are a bunch of Shia Muslims with Shia Iranians as the head

Oh, hey, another example of religious organisations having no principles. Cool.
Not sure why you wanted to bring up people arguing about fiction being shitty to each other as a reason for the PRC also doing shitty things that hurt the world and make its enemies stronger.