Hello,
YubiKey (Passkey) can only be used to log into the web vault at the moment, not the browser extension, desktop app, or mobile app. Some such features are on the roadmap, but it isn’t clear when.
If you don’t have to worry about malware/scams and their computer getting stolen (definitely use BitLocker!), you have more options. For example, Login with Device for both login and approval is available on all clients now. All you have to do is configure the browser extension to “Logout” on “Browser restart” and ask them to never shut down the browser (and maybe even the computer—just sleep or hibernate).
Then, logging in may be minimal (when you restart the browser or the computer), which they can do via Login by Device. They can approve their own logins, perhaps from the mobile which is setup to not logout by default (but do use biometrics), and even if they fumble, but if you have a YubiKey set up with their vault passkey, you’ll be able to log in with the passkey and approve the login for them.
This is one possibility, probably with many variations. Others may suggest more alternatives.