Hey there.
So I didn’t manage to resolve the striped issue in itself. Rendering at 1080p is fine but at 4k that issue starts to happen so I assumed that it was some graphic card issue - which still seems a bit odd to me as I’m currently using a 3080.
The fix that I found was rendering it using the High Resolution render setting just like you.
I didn’t have shading issues tho. I tested this on several render with various types of lighitng and settings. For me it worked really well even being able to render at 6k with super high render speed.