Borderless weird FPS loss

I wanted to play this game in borderless mode to use ACT etc.

Problem is I have 120hz monitor but I play this game with 60fps lock in settings for stability. In full screen there is no problem, stable 60fps but when I change to borderless flat drop to 40fps.

I thought that maybe my laptop is not good enough to play this in borderless with stable 60fps so I tried unlimited option for frames. Full screen 80, after changing to borderless flat drop to 70.

Doesn't it mean that I should have stable 60 fps in borderless mode with fps locked option on?

Here are some screenshots:

locked 60fps fullscreen: https://imgur.com/a/uBEiSLZ

locked 60fps borderless: https://imgur.com/a/czJcm1K

no limit full screen: https://imgur.com/a/MKJLcH3

no limit borderless: https://imgur.com/a/tyKtMC3

CPU: i7-8750H
GPU: NVIDIA GeForce GTX 1070

Edit: Ok, so apparently I solved the problem by ticking option: "disable fullscreen optimalization" in compatibility options which is off by default.