I like FIDO U2F as a second factor, although you always need a fallback of some kind in case you are stuck using a device without a USB port. I don't like it as

I like FIDO U2F as a second factor, although you always need a fallback of some kind in case you are stuck using a device without a USB port. I don't like it as a single factor, as most devices make it hard or impossible to back up your keys. Using Passkeys with Bitwarden is pretty interesting though, and appears to satisfy most of my concerns, as they're just stored in my password manager and move devices with me.