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...
True, I hoped for something better :-/
If it makes you feel better, most PINs on modern devices are hardware backed in some way (TPM, secure enclave, etc) and do things like rate limiting. They’ll lock out using a PIN if it’s entered incorrectly too many times.