You can’t remove a disk from a RAIDZ zpool.
But if you’re removing a disk such that you can migrate the data away from the zpool into that disk and then plan on destroying the zpool anyway, then read on.
In my case. I wanted to switch this particular zpool over to be a simple mergerfs volume, and copy the data from the zpool into it. But I didn’t have any additional (big enough) disks laying around, so incrementally removing disks from the zpool and adding them to a mergerfs while copying the data from one to the other was the approach I used.