I would like to be a bit more certain that at point were the heavilly-rigged IP lLaw (with associated things like EULAs and “by using this software you accept it’s TOS”) crosses with Contract Law, obviously breaking of contract law with retroactive changes is laughed out of court even when the legal argument was made that the Unity Runtime is licensed separatelly from the Unity Editor and as the installation of a game that contains parts of the Unity Runtime is a copy of copyrighted material

Well, I obviously understand you and would say that it is the right thing to do.
And I only talk about my country and by extension think that maybe it is the same in all the EU even if I know that, while there should be an uniform law it is not always that way.

But even if the Unity Editor and the Unity Runtime are licensed separately, this just make 2 license so 2 contracts, nothing else. But both licenses must follow the law of the country they sell it.

then it’s up to Unity to determine the licensing conditions.

Which is true.
What I am saying is that what Unity cannot do is to do a retroactive change to the terms of the license.

However after watching the complete legal shit show that’s been done around IP Law since at least the 90s (note how in almost 3 decades EULAs in software haven’t been clearly and definitivelly thrown out everywhere, given that they’re trying to “change the terms of the implicit contract which is a sale after the sale”), I’m not willing to risk my company until I’m sure.

I mean, if all this was for certainly ruled by Contract Law and only Contract Law, all you say makes perfect sense as that’s pretty mature even in cross-jurisdiction trade relations. However this stuff overlaps with IP Law (as I said, the installation of software in a computer is considered a copy of copyrighted material) and that one has been heavilly rigged and abused for decades, including in situations where Contract Law would seem to apply (EULAs in software being a pretty big one).

I am pretty sure that the EULA in Italy and EU is different from the one in US and the one in other countries.
So probably the EULA I accept is legal in my country and if there is some illegal terms they are void.

You seem to be going from the starting from the point that the Law makes sense and is fair, which understandable … if you aren’t well acquainted with any lawyers ;)

Let's say that I had to interact with lawyers more than I'd liked to.