My question is at Mysterious disappearance of disk space on Catalina (and not any other OSX)
Tetsujin closed it pointing to How can I figure out what's slowly eating my HD space? but just look at the very different O.S.s in the two questions.
Also, my question is vastly different in that I have expressly identified that the Case of the Vanishing Disk-Space is solely attributable to Catalina as no such thing was happening in Sierra, and there are also further particulars stated in the question.
In one line, What on earth is Catalina doing with and to the disk that other OSXs didn't?
With due respect to 'One-Percenters' of apple.stackexchange, please try to read and understand the question and its specifics and don't keep being so trigger-happy in shutting down questions/threads/discussions.