I’m running TrueNAS Scale (Dragonfish-24.04.2.3).
I created a RAIDZ1 (3 wide, 1 spare), been running fine. One of the drives went bad, it emailed me (so the email config worked), by the time I logged in to the TNS dashboard, the spare already took over for the bad drive, and was 1.4% into resilvering.
Now that resilvering is complete, I noticed the spare drive is still a spare.
Replace the faulty drive, Spare goes back to being a Spare.
Remove the faulty drive, such that the current Spare becomes a normal drive. And no more Spare, (or you can add another one later).
Ignore the problem until something else goes wrong
That is one nice thing about ZFS. If you should decide that the currently active spare is the best drive to remain in the pool, just remove faulty drive.
I don’t have the GUI or command line instructions handy to make this happen. But, if you want that, someone here can likely assist you with that option.