At least one spare is recommended for dRAID

[SmallBarky]

It is explained in the documentation you were linked in a different thread of yours. Try to find someone with computer knowledge to translate.

Spares are not a single device but the space is spread over the dRAID.

How to auto resilvered

There’s not a lot of information to go on here, but I think you’re misunderstanding how the distributed hot spare works in a dDRAID VDEV. There is no single disk that is not being used and can be removed. I’d suggest reading the ZFS dRAID Primer | TrueNAS Documentation Hub.