huge system file on an iMac with Mojave

This computer has been upgraded through several versions of macOS and presently on Mojave ? It that correct ?

What is “Other” storage on a Mac, and how can I clean it out?

Free up storage space on your Mac

OmniDiskSweeper Safe to use

How to delete Time Machine snapshots on your Mac

See used and available storage space on your Mac

The final word from Apple on Managing the " Other " Category

• Other: Contains files that don’t fall into the categories listed here. This category primarily includes files and data used by the system, such as log files, caches, VM files, and other runtime system resources. Also included are temporary files, fonts, app support files, and plug-ins. You can't manage the contents of this category. The contents are managed by macOS, and the category varies in size depending on the current state of your Mac.

Ah, inheritance from the Cats time. My first cat was Tiger on the old and trusty Motorola PPC Powerbook. Great machine at its' time.