All guides to deploy using docker mention typing your keys/credentials/secrets into the docker compose file, or use a .env or similar file, I'm wondering how secure is this and if there's a better option.

Also, this has the issue of having to get into the server to manage them, remembering which file has each credential.

Is there a selfhostable secrets manager? I've only found proprietary/paid ones for large infrastructures and I just need it for a couple of my servers/projects.