13" MacBook Air storage problems

My 2014 MacBook Air has 121 GB of built in flash storage. Of that, 1.22. GB is occupied by apps. 710 mb for "music and others", 16.32 GB is taken up by system, and 17 GB is available. 86.73 GB is labelled "other". What that "other" is, I haven't a clue. Getting rid of all documents, applications, messages, photos, etc.only frees up about 3GB. I've tried MacKeeper and Disk First Aid, nothing free up morecthan a few megabytes. And, yes, I have been emptying the trash. How do I get my 86 GB back? Running Big Sur 11.6.4.