UPDATE, MAY 2021:
The above mentioned tweaks do not fix the eyes/nerves issues. I've tested it thoroughly. Mac Mini M1 does have something evil on board. Probably, is has something to do with GPU, because when in Recovery mode, there seem to be no symptoms. Nothing helps, mates. Windows setup for the same monitors (2 different FHD) works great and is a sharp and immediate contrast to M1 pains.
DO NOT BUY CURRENT M1 IF YOU HAVE SENSITIVE EYES OR NERVOUS SYSTEM.