My yubikeys aren't biometric ones, so it's possible I'm wrong about what they support, but I'm pretty sure it's possible to have your SSH key on them and require both fingerprint and password to use it.

https://www.yubico.com/products/yubikey-bio-series/

(And I'm sure they're not the only company who makes such devices, they're just the one I'm familiar with myself.)

Some iOS/Mac SSH clients allow SSH keys to be protected by TouchID or FaceID, https://news.ycombinator.com/item?id=15853345

Might be possible on other systems with a fingerprint reader and TPM, https://news.ycombinator.com/item?id=36920105

You absolutely can.

https://linux.die.net/man/8/pam_thinkfinger

You can do that on Macs with Touch ID