I just tried because you made me doubt, but you can access your passwords offline with bitwarden. Your argument about trusting a third party is far more pertinent, i’m choosing to trust them but thats really my choice. It is also a limited trust: even in a case of a data breach, bitwarden is encrypted end-to-end with your password, even if someone gets access to your data they wont be able to read it without your master key.
Ive worked with thermal printers used in POS, and usually they use a different protocol than notmal printing so you’re not using cups (basically you send “commands” with text and its position). But i am sure there are some exceptions…