I'm sure there are many better alternatives to .env, but its ubiquity and support across various tools makes it super convenient.

I'm using 1Password's .env integration[1] and although the UX is a bit clunky, I really like it. My API keys are secure, tools that ordinarily support .env just work and there's a team-sharing feature too (although I'm yet to use it). It's pretty neat.

[1] https://www.1password.dev/environments