This effort was using a third-party cross-platform password manager.

The specific case was a mobile game that needed to open a web browser that logged into a secondary account system, which I had set up to use passkeys. The in-app browser didn’t seem aware of my phone’s password manager plugin, and so it allowed no way to get in. Other times, logging in on a web browser with the password manager fully working simply gave an error - which could be blamed on the individual account provider, but then if I’m taking a chance on each passkey account, it’s again pointless.