Hello Kishi10,
Isolating the issue is going to be the best way to find a solution.
If possible, test the monitor with another system, or test the Mac with a different monitor. This will help tell you where the issue is originating.
We would suggest that you try to isolate what is causing the problem by starting the system in safe mode.
Here are the steps from How to use safe mode on your Mac - Apple Support:
1. Shut down your Mac.
2. Turn on your Mac and continue to press and hold the power button until you see the startup options window.
3. Select your startup disk, then press and hold the Shift key while clicking “Continue in Safe Mode.”
4. Log in to your Mac. You might be asked to log in again.
The computer will take longer to start in safe mode, and the screen may have some distorted video as it starts up. This is normal. Once you are logged in, use the system and test to see if the issue continues.
If everything seems to work as expected, go ahead and restart the computer normally and test again. Starting in safe mode forces the computer to run some disk checks similar to First Aid. This can resolve some issues.
Cheers.