IIRC it took them a little while to add support, but I was more thinking of stuff like KeePass. KeePassXC has passkey support, but AFAIK none of the Android apps do yet (although it sounds like KeePassDX is getting close, finally). Also, when I was using Bitwarden, I had issues with some services not liking its passkey implementation (despite being fine with Proton Pass for whatever reason). May be fixed now, but it was incredibly annoying at the time.