Okay … well… 3 things… then…
Grab the elbow joint > Tab into Edit mode > hit 7 on the number pad to get ‘top view’ > zoom into the elbow a little > then G > X and slide the elbow joint back (up in your screen) … you have to have some bend in that elbow…
Second… in your Armature modifier check “Preserve Volume”
3rd… add a Subsurface modifier and set it to ‘2’ minimum in view and Render…
the only other thing I can suggest is to not use the Shoulder elbow rotation setup you have and use an IK target for the elbow to help the IK solver with understanding what direction is supposed to be pointed at all times…
I’m sure there are ways to make it better… but I think you should expect some twisting. I check the other rig, and the difference with yours is the length of the foreamrs. your character is a bit more “chubby” and so it’s going to twist. also if you do the same with your hand, you will see that you have a 270deg of twist, but it’s not from the elbow, it’s from the shoulder. Meaning that when you do it, your elbow rotate too.
So for your rig, you can take that into consideration.
I had this issue before when i downloaded some other persons rig to use for my own project. You need to reduce the bone “segments” that option is found under Bone–>“Deform” --> segments.
This behavior your getting is good for objects that require twist but skin does not visibly twist like that unless a large force is applied.
