212 GB of System storage on Mojave suddenly in the last month
I have no idea what is going on here. The closest I can find is that it is PROBABLY Time Machine Local Snapshots not deleting but I can find no way to turn off Time Machine or delete those Snapshots on Mojave, it's all for High Sierra.
The Time Machine support page does not feature a way to turn it off.
MacBook Pro 13", macOS 10.14