xcrun simctl delete unavailable
Deletes all 'unavailable' simulators in Xcode.
An 'unavailable' simulator is one that you have never used before or that you don't have the SDK installed for. They are safe to delete because simulators can be redownloaded. You will also not lose any data on them because you have not touched unavailable simulators before.
I found this trick in a Reddit post by /u/LisaDziuba here. Using this trick I managed to free up slightly more than 10GB of space.