Well I happened to be looking up some mackintosh related things regarding custom display resolutions, but this should theoretically work on a genuine Mac, though with 8k I'm not so sure. I was messing around with making Luna Display work in hidpi with 3 other displays.
https://www.tonymacx86.com/threads/adding-using-hidpi-custom-resolutions.133254/
Need to download IORegistryExplorer and it's mildly technical but might be worth a try.