Can I do hardware attestation across several devices yet? My desktop, my phone, a console, my girlfriends phone of a different brand if I need to log into a shared account, etc?
It seems like one of those things that only works if you're sticking to one ecosystem.
Yes. You can register as many different passkeys as you want. Any limitation in passkeys registration quantity is a limitation of the website/app itself and not a limit of the spec, etc.