With Bitwarden, you can use passkeys on chromium browsers. Vanadium actually enabled support in advance.
You need to have Play Services installed, though. This is due to Chromium, nothing GOS can do about that. No need for even network permission for Play Services, luckily.
Firefox is supposedly adding a standalone implemetation, which won’t require Play Services, any year now…
Don’t have Proton Pass, so don’t know what’s the situation there. With BW+Vanadium, they work well. I just wish Play Services weren’t required. With Google Passwords they probably just work.
They are convenient, but there’s only a couple sites that support full login with passkeys. I’m reading between the lines of your comments none of them are sites you’d use (Microsoft, Github, Google, etc…)
Someone else commented KeepassXC has an open issue about passkeys, perhaps they’ll add support sometimes too.
You’re not really missing anything yet, to be honest. I’ve mostly tried them out just out of interest, and it’s still very much aimed at people using Google or Apple…