Input lag disappears for ~30 seconds when plug OR unplug any USB.

[InputLagger]

UPDATE: Hopefully the last one I have finally fixed it. It was actually caused by my routers power supply - it was faulty and it was injecting EMI into my power grid, when I tried with ethernet unplugged I still had issues, after replacing the routers power supply with another one, everything is perfect

Which specific router do you have and what power supply have you swapped to?

I have Huawei HG8145X6-6Te, I have 2 switching power supplies that came with the ISP, one for router and one for TV box, changing them after a while makes lag disappear but it slowly comes back, I tested for a full day without it and it was perfect the entire time, so I'm 100% sure it's the cause. Switching power supplies are known to leak EMI. I ordered IFI iPower2 and will give final update after 10 days for example that everything is fine.

I couldn't figure this earlier for multiple reasons - when I unplugged ethernet cable the lag was still there, so I immediately discarded possibility that it's router related. When turning off every breaker in the apartment I always left the router one which was in the living room, the cables were routed there so I couldn't put it in the same room as the PC.

Another weird observation that lead to this discovery is that the router's power supply was in the same power strip as the TV, TV Box and some generic standing lamp. When I put the router in a power strip where it's alone the floaty mouse was completely gone, the screen was not smooth still and there was desync, but the floaty mouse isn't coming back when it's alone without other devices. The fact that the floaty mouse isn't coming back and that everything is 100% perfect when that single thing is unplugged makes me sure it's the sole reason for years of problems, I'm not sure if anything in my apartments wiring and stuff like that contributed to it tho.

The final update?