When the British expelled criminals to Australia they couldn't return home. Was Australia not a colony? A ton of European immigrants to the American colonies intended their journeys to be one-way trips, and were functionally barred from returning by cost. Does that mean there were no colonies in the Americas?
Besides, throughout history you almost never see settlers leaving en masse when colonial administrations end. Sure, some recent arrivees may turn around, and some administrators who moved there mostly to work in the colonial government may leave, but you really never see the main body of settlers leave. You didn't even have this in South Africa. They simply have to live under a government where they can't shoot the locals with impunity.
That doesn't really address the point though... Israel is independent, and was so from the start. It's not bound to any other western country's rule, which is the first requirement for being a colony.
the vast majority of its citizens don't have citizenship in any other country and have literally nowhere else to go. Therefore it's not a colony
It directly refutes this.
If you're leaning on Israel being formally independent, they're about as independent from the West (particularly the U.S.) as a college freshman getting their tuition paid by Mom and Dad. No one here is talking about Israel being independent on paper, we're talking about how it interacts with other countries in reality.
My point is that Israel is not a colony and has a right to exist.
I am not excusing what is being done to Palestinians. I strive for peace, and Israel is showing no signs of it anymore, though it absolutely did just a few decades ago. But no one is saying all of Russia doesn't have a right to exist because it attacked Ukraine. No one is saying USA or Canada don't have a right to exist because of how they historically treated and are still treating native Americans. And no one should be saying that Israel doesn't have a right to exist.
Coexistence is the only solution. It seems impossible today, but it's the only possible solution that could possibly work. Anything else is even more detached from reality.
The absolute minimum Isreal would have to do to even be said to be interested in peace - let alone striving for it - is to either recognise Palestine as a sovereign country and treat it as such, or to recognise Palestinians as citizens of Isreal. So long as they keep holding them in this limbo, in egregious violation of international law, Isreal has zero interest in peace.
"No country is fully independent" says nothing about whether Israel is properly classified as a colony. It's a platitude.
a right to exist
Another platitude. What do you mean by this? Israel's current actions are indefensible. Many of its past actions are indefensible. Its policy of neither recognizing a Palestinian state nor granting equal citizenship to Palestinians is indefensible. It must either fundamentally change or be replaced by a government worth supporting, like South Africa before it.
It certainly does not have a right to continue existing in its current form, no more than Nazi Germany did.