While I still don't agree that ending up with a partition of the wrong size and type is a copy, the fixes aren'tweren't too complicated:
- Change the partition type to Apple APFS using
gdisk - Change the partition size in the GPT back to what it was originally, using
fdisk. This works for APFS partitions since GParted couldn't possibly have resized the actual file system to span the whole partition (no stable APFS write support as far as I know).