We had originally planned to go all-in on passkeys for ONCE/Campfire, and we built the early authentication system entirely around that. It was not a simple setup! Handling passkeys properly is surprisingly complicated on the backend, but we got it done. Unfortunately, the user experience kinda sucked, so we ended up ripping it all out...
I am very shitty on security (I would not write this reply on a post on the cybersecurity community), and I resisted MFA for several years as being too annoying having to login to mail/SMS. After finding open source apps supporting TOTP, I feel better about it and I manually do the syncing by just transferring the secrets between my devices offline.
Passkeys are another foreign thing that I think I will get used to eventually, but for now there are too many holes in support, too much vendor lock-in (which was my main distaste for MFA, I didn’t want MS or Google Authenticator), and cumbersome (when email and SMS were the only options for MFA, difficulty of portability for passkeys).