Clicking on my saved passkey when trying to log in with the recommended Proton Pass extension results in the following error:

A similar error also shows when you try to add a new passkey.
This functionality works fine in Safari and Orion Mobile.
I expect Passkey support to work
Version 0.99.130.3.1-rc (WebKit 621.1.2.111.4)
Sequoia (15)