4K display has known issue that is unrelated to Qubes but is worth mentioning. Sleep/hibernation will cause display issues that may trigger epileptic seizures, solution is to disable that functionality and preferably use external monitors for UX reasons. However, problem persists through reboots, and requires some time powered off to cease. For that reason, I specifically use external monitors.
In 4.1.2 stable ethernet card had the PCI reset issue, solution is in No network after install - #8 by Sven
So far that is all I’ve run into, but if there are more things I can test help fill in gaps let me know.
Currently using thunderbolt 3 dock with displays, only complaint there is trying to disable the laptop display causes so much lag that I can’t save the settings in time so the settings revert.