MacMini 2018, OS Mojave 10.14.6
Following on from Sooz's thread, I checked my MacMini's drive after being warned it was nearly full. It has a 250GB drive and when I checked storage it told me it contained 8.04GB for Apps; 201.96GB for System; "Other Volumes in Container" 2.84GB, leaving 28GB available. All videos, photos and documents are on external drives.
So what is clogging up the system?
Only other thing I can think of is Mail attachments, but those are generally small things like PDFs and cartoons, photos, etc.