Python Software Foundation survey finds that a significant number of Python developers are still using Python 2 for data analysis, computer graphics, and devops.
Java has had some breaking changes, especially the move to Jakarta namespace for certain dependencies, (thanks Oracle trademark enforcement) but I have had other code taken from 9 to 19 with no changes at all. I have some dependencies that I haven't recompiled since 6 which still work in 19.
Now dependency dependencies, yeah that can get tricky to get them all the right version.
I very much doubt that you can run old code unchanged on newer Java versions. Especially not without dependency updates
This problem is not exclusive to Python
Java has had some breaking changes, especially the move to Jakarta namespace for certain dependencies, (thanks Oracle trademark enforcement) but I have had other code taken from 9 to 19 with no changes at all. I have some dependencies that I haven't recompiled since 6 which still work in 19.
Now dependency dependencies, yeah that can get tricky to get them all the right version.