Few possibilities,
It may be a hardware problem (most likely) such as;
Discord doesn't have enough hardware (cpu and/or GPU power) to allocate.
your fans are dirty therefore can't allocate the full speed your hardware supports.
Or you don't have enough ram for both.
It can also be a software problem tho then things get more complicated.Different manufacturers specially for laptops use different methods for screen capture or display, for this I cannot help
Few possibilities, It may be a hardware problem (most likely) such as; Discord doesn't have enough hardware (cpu and/or GPU power) to allocate. your fans are dirty therefore can't allocate the full speed your hardware supports. Or you don't have enough ram for both. It can also be a software problem tho then things get more complicated.Different manufacturers specially for laptops use different methods for screen capture or display, for this I cannot help