I use it on Android and it's always been a Bitwarden-specific pop-up that shows up on password fields. Maybe with accessibility mode it would work as you mention? Ok that's a new thing to test.

I assumed that the accessibility one is non-standard and Bitwarden's uses the system native one. Because I see Bitwarden in passwords and autofill in settings (or something along those lines). I find it to work way better than on iOS anyway.

I don't think that the visual indication means they aren't using the system way. The accessibility service is probably not a good idea given how much control it can give the app over your system.

Yes, Bitwarden definitely advertises itself as a password provider within Android's built in password/passkey manager API. I see Bitwarden appear in the list of saved passwords in the native UI along with Chrome which I have set as secondary.

Otherwise I'm not sure how Bitwarden saved passkeys could even work at all without using the native integration.