I think what you describe fits JS better. Already migrated your router library for your react project, this month? What, still not migrated!? No one is building things for X any longer! You need to switch to Y asap!

I am not aware of anything in current Python 3, that has broken backward compatibility to an earlier Python 3.

Some dependencies are implemented in ways, that will require you to use newer Python versions. Often those are packages, which are glue for lower level libraries. Like tensorflow.

Perhaps I am describing the same thing as in JS ecosystem. But for some reason neither have I migrated to another way of defining my API routes in Django lately, nor have I had any need to in the last couple of years. I guess in the JS world there is just so much more half-backed stuff that gets hyped to no end, and this job guarantee is celebrated as "quick evolution".