LG Ultra Slim DVD drive not working with iMac 21.5"
I had the same trouble as some other folks on this issue.
Sorry if this is obvious but, 2 things:
1) Make sure you use the cable that came with the drive - others may seem to fit with drive, but may not work.
2) Nothing shows up on the desktop until you insert a disc.
iMac 21.5″, macOS 10.15