For me, in Reverse, the rear camera is rock solid. Same for in Park, selecting the rear camera manually. I just went out and looked at it carefully. The two small side camera views do have a very slight flicker but no jitter. This is so slight that had to get up close to notice it. I suspect it's the resizing and conversion of the 36 fps cameras to whatever the main screen refresh rate is (60 fps?).
Looking at the rear camera there is some noise, as it is dark in my garage and it's pointing at the garage door. That goes away when there is more light around.
It may be some people notice this flicker more than others. Not sure there is much that can be done. HW4.0 may have cameras that can do 60 fps (and an AP processor that can handle it), which could eliminate the flicker. No idea when HW4 will go into production, perhaps in 2023.
So one big question - are you seeing jitter (the entire video moving up/down or side to side) or is it flicker, where the image is getting slightly darker/lighter? Also, is this at night or during the day? It may be more noticeable when you have external LED/Fluorescent lighting that flickers at 30 Hz nearby. See if it happens in daylight.