Do you use any native plugins? Or if you use .Net plugins, can you DotPeek at them and check if they use Marshal.AllocHGlobal? Besides fragmented and unmapped & remapped unused managed heap pages, those’d be the typical user side sources for Untracked memory.
Also I did a bit of a write up of how to analyze untracked memory on windows here, and while you don’t have that issue on Windows, the parts about which kind of callstsacks to discount holds for Mac as well. So if you use Instruments to profile the Editor following the guide Alexey shared above, you might be able to get a better understanding of what’s going on there.