It is unclear what Add Recovery Key does as it does not perform the same actions as the legacy UI
See attached screenshot for example.
The old UI did this:
This screen prompts for root's password and then the directory in which to save the key.
I tested like this:
root password: test
rekey password: yetanother
This screen accepted the password I supplied (which was neither the root password nor the passphrase), never asked me where to save the key, then indicated the pool was successfully rekeyed.
In other words, I have no idea what the system actually did, what got stored, and when it expects the password I input.
The tooltip is also useless, but can't be updated until we know what this action is actually doing.