I made a test on a clean SSD: Win 10 20H2, no patch, drivers up to date, only DCS > same problem.
Without V-SYNC > massive stuttering (monitor 100 Hz)
With V-sync > monitor 100 Hz > massive stuttering
With V-sync > monitor 60 Hz > OK, no more stuttering
With V-sync > monitor 100 Hz, monitor 2 (60Hz) unplugged > OK, no more stuttering
I tested previous Nvdia drivers 465.89 > all is back to normal
With V-sync > monitor 100 Hz and max 100 FPS, monitor 2 (60Hz) plugged > OK, no more stuttering