Hi again,
we REALLY gotta talk about how hard it has become to use FIDO2 Sticks even if you want to (or a service requires them) rather than platform or phones or password managers, or anything else I might have forgotten.
Several combination need you to go through a bunch of steps that are not immediately obvious that they exist without prior knowledge, and some even require you to actively make steps that are quite literally against what anyone would assume, like clicking CANCEL.
1) if you are on windows 10 and use a chromium-based browser, and have bluetooth if you cannot use windows hello (either due to restriction by the relying party or not having it set in the first place), it will show a dialog like this:
(ref: attachment chrome-passkey-phone.png)
just store the passkey on phone with NO INDICATION AT ALL that you even can use a FIDO2-Stick, here you have to click the "back" button at the bottom left to get a choice dialog between External or phone.
2) no preference set by the RP, Windows hello active on Windows 10, you get this absolute beauty
(ref: attachment W10-Winhello.png), where you need to click CANCEL
3) Macos, a Browser that is not Safari, you get this dialog if there is no specific preference, where you also need to click cancel
(ref: mac-passkey-altbrowser.png)
4) with safari it is ever so slightly better, offering a "more options" button, but still why doesnt it ask where to store directly?
These are just some of the worst that I aware of, there are easily more especially with password manager extension hijacking the request even if e.g. cross-platform has been set or Browsers' own password/passkey managers, such as chrome.