Yeah, you are not wrong. Also, although I recently moved off of Mac to Linux for most desktop computing, I think I tried every single remote desktop solution f

Yeah, you are not wrong. Also, although I recently moved off of Mac to Linux for most desktop computing, I think I tried every single remote desktop solution for macOS over those years. The best thing I ever found (in terms of being able to remote desktop into a 5K display and have usable latency and at least eventually show the screen at full resolution) was AnyDesk. For my last year on the Mac, that is what I recommended for remote desktop. (It does work on Linux too, but on Linux I find xrdp works fine, just like on Windows.) One tip: If you are connecting from macOS, using Microsoft Remote Desktop, that app crashes with 6K and 8K screen sizes. But there is an app called Royal TSX which can be an RDP client, and it handles those resolutions fine.