Edit: This post no longer reflects my current opinion. I have been able to install display drivers on Windows 8.1. Also, 8.0 has very different rendering than 8.1 after further testing.
Windows 7 is working on my XPS 7590 Intel 9th Gen laptop. Only thing is it needs USB Wifi, since the internal adapter has only Windows 10 drivers. Standard VGA driver is running it at 1080p native resolution.
After a lot of testing I found that 8.1 and 10 1507/1511 have almost the same rendering (which is really not that bad compared to modern OS), maybe 10 is a bit cleaner, but it's not that noticeable. As we already know 1607 is when it dramatically changes. The only reason I bring this up is that if 2015 LTSB is not tolerable 8/8.1 are not likely to be tolerable either. But 8.1 specifically has the advantage of running .Net 4.8. 2015 LTSB can only do 4.6.2.
But 7 is its own beast. I find it tolerable on the Standard VGA driver in a way that 8/8.1/1507 is not. With drivers installed it's not as special. That Standard VGA driver seems very limited in a way that is good for me.
Standard VGA Driver > Basic Display Adapter (8/8,1, early 10) > Drivers on either
I still want to do something with XP again. That's my next project. I want to transfer material for offline viewing on to an XP machine. It doesn't have to go online.