If I play a game on one monitor and watch a video, is the frame rate inconsistent on the other?

I have had a problem for a long time that no matter what I watch on my 2nd monitor, i.e. Youtube, Twitch or Netflix, the game that I play on my 1st monitor does not feel smooth. I would even say that at 144 fps I only have 60. I have a 144hz monitor as the first monitor and a 60hz monitor as the second. Are there any connections and how can I fix this?

Do you have a graphics card with 2 outputs or 2 cards? And above all, which ones?

Of course, if you watch a video on the second monitor, it puts a strain on the processor. If it is not a particularly strong CPU, it can cause poor performance.

So I have a 2060 from MSI and both screens are connected to it

If one of the monitors only has 60 Hz and the other has 144, it can also be the case that the card then turns down to 60. I do not now know exactly how it is with your card.

If you find a setting somewhere --- V-Sync / on / off… Try changing it there.

I honestly don't know if it still exists today. V-Sync on means that the monitor is giving the card a return signal. Only when the previous picture has been completely assembled does the card output the next picture. As a result, the images are also shown exactly sharp. However, a bit jerky even if the hardware is too weak.
Modern HD films… Then all the scripting at Netflix and the like is already dragging performance…

Then when there's a game that performs well… Well…

Oh well… You can also try to operate the first monitor on the display port and the second with 60 hz on the hdmi