When 1Password prompts to use a passkey for authentication, Orion should support pressing the return key to use this passkey (as in Chrome):
This would make it possible to login solely using the keyboard (Cmd+\ or down arrow to select a username/password, return to submit, and return again to use passkey).
Google Chrome & Brave support this and logging in using a passkey is possible without taking your hands off the keyboard to use the mouse, navigating to the passkey dialog and clicking Sign in.