TOTP codes are typically six digits long and change every 30 seconds.
They are derived from a shared secret value and the current time.
Your computer time must be synchronized with an internet time source to generate valid TOTP codes, read more here.

TOTP Generator

KeepassXC

Once set up, KeePassXC can calculate TOTP codes like any authenticator app, such as Google Authenticator.
The codes can be used with copy/paste, browser extension, and Auto-Type.

This comes with a huge caveat :
generating your TOTP (timed one-time password) codes ==in the same database as your passwords== essentially defeats the purpose of TOTP secrets.
Still, it’s better than not using any two-factor authentication (2FA) method 
since at least you’re protected from anyone who manages to learn your password without accessing your vault.

For good security, though, the approach is to create ==a separate database for your TOTP codes==
The database must have a password different from the one for your passwords.

If you’re already using an authenticator app you like, you’re probably better off sticking with that.
The benefit it adds is avoiding needing a separate app for 2FA codes.