I don't use them much because I don't have a good way to register them and use them across device ecosystems. I use all three OSes regularly.
Or treat it as an opportunity to try to avoid "vendor lock-in"/increase redundancy by using all three to have 3+ passkeys in every service. Windows 11 can act as useful a bridge for bootstrapping all of your keys into a service: register for a site first on iOS or Android, use Windows 11 bluetooth to login via the first passkey, add a Windows passkey, and use Windows 11 bluetooth again to add the third. (Or some combo of that with the Windows iCloud Passwords app and/or Chrome.)
[1] https://www.smokingonabike.com/2025/01/04/passkey-marketing-...