Hz of main monitor are unstable


I have 75Hz monitor, I have set it in system setting but when I go to pages that shows me my refresh rate it usually jumps between 74 and 76. And also games when I use Vsync or limit FPS they still don’t look smooth. None of this happen when I set 60Hz in system settings.

Additional note: I have 2 monitors and 1 TV plugged in, everything has same resolution which is 1920x1080, secondary monitor and TV has 60Hz and the TV is mirroring the primary monitor.