>Backwards compatibility I understand, but which languages give forward compatibility?

Python used to offer it frequently. from __future__ import ...

Code written in C89 can trivially link against code written in C18. This also mostly works in C++ as long as new features are not used at the interface level and you don't have an ABI migmatch (e.g. with stdlibc++ std::string, although that's possible to work around with proper configuration). Any language exporting a C FFI should work just fine.

Hm not exactly what I tried to convey. I guess I would love if python stopped trying to add new syntax so often.

Walrus operator, fstring, etc. should happen maybe once every two years ideally? Did we really need the walrus operator? The cost of adding it is making any library using it in python 3.8+ incompatible with runtimes of python3.8<.