Some tips for stuff that give cloth room indigestion. It really hates long narrow polygons. These are frequently used to create modeled in edges on cloth like a hem or piping.

It also hates sudden movements. T-pose to sitting in 1 frame. Act it out your self and see how long it takes you go from standing to sitting. Even if you just plop down it 1/2 to a full second. Give the cloth sim 30-60 frames to get in pose.

Non-manifold shapes. That's "T" shaped geometry. That's a patch pocket or modeled belt loops that connect to the underlying mesh. Leave the pocket un-welded from the base mesh and add it to the soft decorated group in the sim instead. Non-manifold geometry is a no-no in many modelers too.