The problem with "sites must allow you to have multiple passkeys" bullshit is that sites aggressively push you towards making that first passkey, but then hide the process for adding additional ones 6 layers deep in settings such that a typical user will never see it.

I literaly just had to unfuck my grandfathers webmail because of this garbage. "oh, I can only log into my email on my ipad now" and I immediately knew the shadowy cabal of evil over at the FIDO Alliance were to blame.

It is up to us technical users to make sure the other 90% of society don't fall for this shit. Tell them it's the mark of the beast, tell them that it's fascists seizing control of your identity, tell them whatever will make them run for the damn hills anytime they see "alternative ways to sign in".