@mcdonc - tell me what monitor setup you have. I use a HiDPI laptop with a regular monitor and I have some scripts that will scale and reposition the regular monitor so that you can still have HiDPI where it matters
Thank you! You tried to help me before with xrandr config at HiDPI and Multiple Monitors - #3 by mcdonc but I just lost patience trying to mutate your config (and others') to my specific setup (left-to-right, laptop monitor is 1080p, one external monitor is 2560x1440 natively, other external monitor is 4K). TBH, the only reason I was trying to get it to work was because I figured that downsetting to 2560x1440 would cause the rendering look blurry on my 4K monitor, but in reality, it looks as good as my non-4K monitor anyway, so I retreated. 
Our best bet is to wait until we have GTK4 running on Wayland, but it'll be a few years before any of that happens on MATE. It's currently too tied to X11, and we just finished migrating to GTK3. Not to mention that neither Wayland nor GTK4 are really ready yet...
I'm not worried about it, and maybe I can even help with that effort if I learn enough before it starts in earnest.
Thanks!