[varjolintu]

If you consider KeePassXC to be one of the big players, they (will) support importing and exporting Passkeys.

[DavideNL]

...and if i understand correctly, websites can dictate whether they allow KeePassXC (or any other specific vendor) to store their passkey.

In other words, if a website doesn't like that their passkeys can be exported, they can block KeePassXC.