Just a requirements.txt that you can install with pip in a venv works 95% of the time. Unless you need a specific python version, which you only figure out halfway through by reading the documentation. Or you are using pytorch, because on windows and linux the version on pypi lacks GPU support, but there's no good way to encode the download url in your dependencies. Or when people don't properly maintain the requirements.txt, because you are supposed to somehow manually keep it in sync.

I run into some kind of packaging or dependency problem for basically every non-trivial project. Hence the many "solutions", but somehow most end up worse than the problems they attempt to solve