Try to enter about:config in the address bar and set security.webauthn.enable_macos_passkeys to false.

Try to enter about:config in the address bar and set security.webauthn.enable_macos_passkeys to false.

I was able to set that setting, now I guess I'll wait and see if I stop getting annoyed by those prompts.

What will I need to do when I'm not on a mac?

Nope, some sites are still prompting for passkey creation, including homedepot.com

Did you close (Quit Firefox) and restart Firefox after changing the pref?

I have same issue. No idea why pref is only for mac. Changing it on windows and restarting browser does absolutely nothing. This is annoying because I confuse passkey info with saved credentials or create password popup. Only way to disable it, is to completely disable autofill.