this means that if Unity sends you a bill, you don't have to pay it, and if they take you to court, you prove that you're acting within the terms of the license you agreed to, which keeps your lawyer fees to a manageable level because you already have all the documents you need: the contract and your source code.
If it affects your rights then yes. It's not just that they're sending a bill. For example, if it is illegal to change a TOS to suddenly charge for something that wasn't in your jurisdiction then it's probably affecting "your rights".
Even then, it only says the current calendar year. They're making the pricing change on January 1st, right? If so then you're probably out of luck.
No, because if you download it right now, you'll be agreeing to the current terms which no longer gives you permission to ignore new terms as they are released.
Up until now, you could continue using the old engine and never agree to newer terms, and that would be defensible in court. Now, even if you do not update and do not click agree, they will still take you to court and send you a bill, which you probably will have to pay.
Use what, Unity or the ToS? Assuming you meant the ToS under the old version you could stop using an updated ToS only if it violated your rights. (Which is such a weird thing to even mention, if a contract violated your rights then it probably already doesn't apply.) You can stop using Unity whenever you want though because you have free will. Not trying to be sassy about that last point, just explaining why I think I misunderstood you lol.
Yeah, I thought the ToS hadn't changed yet, but it seems like the "no upgrade" clause already got removed in April. I guess their move is to try and force anyone with more than the max revenue/installs to upgrade to a higher subscription to get the lower royalty tier... and lock them in there, because what if you stop paying the subscription? Do you fall to the free version royalty tier? Quite a dick move.
You cannot update to a modern version of unity, or install any unity version anymore technically. I think bc they outline the ability to use the license without updating versions you should be okay.