If you don't need a proper second factor, just set up TOTP and store it in KeePassXC. There is little benefit to a WebAuthn/FIFO "key" stored in your password manager over a password manager with your TOTP stored in it -- almost all of the benefits of WebAuthn (making phishing much harder) already exist with password managers that auto-fill.

There are usecases where you need proper multi-factor authentication, and in those cases you are either a professional (meaning you can handle backups yourself) or you're working for a large company where the management of the keys is done by IT and normal workers don't have to care about it.