Off the top of my head, nothing in that project used python 2.7 exclusive code and pygame_sdl2 hasn't removed any functionality. I'm also able to run the pure python implementation inside Ren'Py 8, although I haven't tested the others. If you're trying to compile the code using cython 3 it's probably not going to work inside Ren'Py. Ren'py currently uses an old version of cython and you have to build against their target cython version. However, I haven't tried building cython code that's compatible with Ren'Py 8 so I can't say for sure. I can't give you any other advice without seeing the code you've modified and/or what you're trying to do to compile the code. Please open an issue in that project's github project with more information.