Why fps is 30 in full screen mode in Overwatch

Solution 1:

I tried solution here but fail.

https://us.battle.net/forums/en/overwatch/topic/20760796904

So I go to settings and pick borderless window.

There I saw that the resolution for overwatch is too high. It should be 1920 1080.

It seems that when I changed monitor, overwatch automatically uses high resolution thinking that my resolution is higher.

My monitor natural resolution is 1920 1080 but it can accept the higher resolution.

Overwatch try to show higher resolution which is, of course, useless.