dotenvx is a way to encrypt your secrets at rest. It's kinda like sops but not as good. https://getsops.io/

Notice how their tutorial says "run 'dotenvx run -- yourapp'". If you did 'dotenvx run -- env', all your secrets would be printed right there in plaintext, at runtime, since they're just encrypted at rest.

The equivalent in vercel would be encrypted in the database (the encrypted '.env' file), with a decryption key in the backend (the '.env.keys' file by default in dotenvx) used to show them in the frontend and decrypt them for running apps.