> Element X has a single field, that supposedly takes both passphrases and recovery keys, but if I enter the recovery key I'm directed to a "Verify with another verified device" screen, even if I had logged out from all other sessions.

I have just tried this on Android.

I am directed to

1) "Device verified - Now you can read or send messages securely, and ... - [Continue]"

2) "Help improve Element X ... [OK] [Not now]"

3) list of chats

Element X Android fyi. No problems logging in using Firefox.