Question Can't get my main monitor to the maximum 165 Hz in dual monitor setup, while I can with single monitor setup.

[iBlueWolf]

I have this Dell S2721DGF 165Hz 1440p via DP.
I also have a 2560x1080p 60Hz ultrawide second monitor via HDMI.
and this "old" 1060 3GB GPU.

My problem is that I don't get 165Hz while having dual monitor, but I can get the 165 Hz having single monitor, is that normal?
Is that a gpu issue, I guess?
How can I know if a gpu can hold both monitors while having 165Hz at the main monitor?

 

[Buljic]

When you set dual monitor setup, max refresh rate of 144Hz one is 60Hz, am I right?

 

[iBlueWolf]

Update: I have tested it deeper and sometimes when i boot up my monitor It will just boot up at 165 Hz and other times at 120 Hz. (when single monitor it will always boot up at 165Hz.)
It never boots up at 60 Hz.

When you set dual monitor setup, max refresh rate of 144Hz one is 60Hz, am I right?