I’m not an expert, so this is an oversimplification, but:
Passkeys are essentially like authenticating the same way you do via SSH, but with websites. The site will use a public key for your account. Your passkey holds the private key. That’s it, as I understand it.
The advantages are that your accounts secured by passkeys will be inherently more difficult to crack than even the most complex, random passwords and it can’t be phished (if you’re using a physical passkey).
The disadvantage is that the standard is still being worked on, and bad actors (MS, Apple, Google, etc.) are eager and willing to sucker people in to using their vendor lock-in software implementations of them. If you want to avoid this, either use real, physical FIDO-capable hardware authentication keys, or use a FOSS password manager that is capable of emulating them.
Pretty much. I suppose that’s a very real disadvantage to using physical passkeys. If you lose it, unless you have multiple passkeys configured, or have access to an account recovery method, you lose that account.
But, like you mentioned, using Bitwarden would sidestep that issue, and they do support passkey emulation.