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…
Nextcloud notes, but the setup isn’t obvious:
And you have a shared note. The Notes folder refers to the folder containing the user’s note files, not sure what the English name is.
Not sure how well concurrency is handled, as Notes doesn’t really support sharing, but if it’s for groceries, I doubt it’s a frequent issue. Has been working well for 2 years now.