Doing some extra 🙂 google research in the meanwhile, if I understood correctly the issue is connected with bluetooth usage (keyboard, mouse, trackpad), since both BT and WiFi use "similar" GHz range, and all those other microwaves (microwave oven, neighbours wifi...) are making that extra noise.
Could this also be connected with this topic issue? I mean, I haven't tried with wired keyboard/mouse, but how do you know that Mac is running but the video card is just not displaying anything?
Some people resolved this issue by installing Wifi router that works on 5 GHz...
I resolved my Wifi dropout issue by switching to ethernet LAN 😟
Since I have BT keyboard and both Magic Mouse and Trackpad, my next step is to replace keyboard with wired/USB one (alu with numeric) and sell Trackpad, but I'm keeping Magic Mouse as there is no other mouse with gestures like this one, and it just sits nice in hand. Or is there? A wired/USB one?