Comparing 1v1 to 4v4, the main difference is for me that I have less things I HAVE to do in a set amount of time to be somewhat competitive in a team game. The stress of 1v1 is simply due to having to do too much.
It becomes (partially) about being the best at doing the most, instead of being the best at the core aspects of a strategy game - I have to compromise/prioritize so much that I just get annoyed that I know what I should do, but cannot. Of course, I have very low APM, so I might be more affected than most, but I think it is still valid as a principle - less things that require fast and continuous clicking means less stress:
-Maps with no mex-clumping: Much more to react to and having to constantly micro units, meaning more stress to do that while also scaling
-Fully open/large maps: Same reason as above
-Navy, land + air all at once is stressful (more so for lower ratings because they generally are lacking the right hotkeys to deal with it)
-a COM is much more valuable in a 1v1 and yet, you basically cannot play without risking it (and micro-ing it) causing more stress and intensity (because of the fear of snipes or mis-micro). I dont really love this suggestion myself, but it might be a solution to make the com do less damage but have much more health in 1v1's. Gives more time to react, without it becoming OP.
-Small, manual reclaim chains: Huge APM drain from the very beginning so that when other things take more micro later, one is already getting somewhat fatigued