I cannot figure out how to source the .env file

If you have ever used the /admin interface to change the config, then it will create a config.json within your data directory. And those values will override everything which is set via any ENV option.

I think the binary only see .env in working directory, current directory.
I tried copying the .env file to where vaultwarden binary is or renamed it to vaultwarden.env, but it didn’t see the file.

Also since it’s only logged as info, it probably didn’t see missing .env file as a problem.