We had originally planned to go all-in on passkeys for ONCE/Campfire, and we built the early authentication system entirely around that. It was not a simple setup! Handling passkeys properly is surprisingly complicated on the backend, but we got it done. Unfortunately, the user experience kinda sucked, so we ended up ripping it all out...
Actual zero knowledge encrypted password managers with 2FA?
Keepass?
Or Bitwarden (supposedly)
Bitwarden is an online password manager and no I don’t consider self hosting it offline.
A sufficiently strong password and additional TOTP should protect you well enough.