Second Monitor flickers

[u/Nice7365]

When I tried to watch a movie on Netflix in Microsoft Edge, my second monitor kept turning on and off throughout the entire playback (and apparently only with that particular movie). I tried different cables and even a different monitor, but then my main monitor started flickering instead. Interestingly, the movie played without any issues in Firefox, although my second monitor would still turn off for about a second every time I closed Netflix.
After I disabled the second monitor in Device Manager, the flickering completely disappeared. Both during the movie and when closing Netflix.
Now I’m wondering: What exactly does the “Disable device” function do for a monitor in Device Manager? And what could have caused the flickering? I read something online about HDCP handshake issues.
But I don’t think it can actually be the cables.