I must say I didn’t test this recently (again)… @LiamRetrams are you sure it worked recently on desktop, specifically on the web vault login page?
Well, I think this was the initial idea… but I can remember saying @Micah_Edelblut that this could be changed when “Login with passkey” gets out of Beta (and the tag/status “Beta” is removed now):
And additionally, at least on the Android app those guardrails are already removed. One caveat: I didn’t try it for the same BW account, but just storing a BW-login-passkey for a BW test account in my regular BW vault. And the latter worked. And I can also log in with that vault-passkey on my Android device. (of course, since the BW vault doesn’t support PRF, I have to enter the master password then)