The concept is fine, but I'm a big fan of doing it with mise instead. It does the exact same thing plus a lot of other things really well. The environment for a project is not just things that get stored in environment variables, it also includes specific versions of tools, common project tasks, git hooks and such. Being able to manage all of that in one place ends up being really useful.

I also really like that for sensitive variables (AWS tokens, prod DB passwords, etc), I can keep those in a dedicated secret store (I use 1Password for personal projects and there are more enterprise focused alternatives for work).