Regarding the overheat protection for stills, I haven't heard of a single person ever bringing this up while reviewing or shooting with the camera, so I think this is a non-issue. This basically holds true for any camera regarding high temperatures and high ISO, and I think a majority of this is Canon just being proactive due to the 8K creating a lot of heat. I highly doubt this will turn into an actual issue unless you leave your camera in a scolding hot car all week and then pull it out expecting to take 20 second ISO 51,200 photos, and I'll definitely put this to the test in some hot weather this weekend, but I've never encountered this with the EOS R or 1DX mark II even in the hot sun all day.
On the Canon Europe Specs page:
Canon EOS R5 specifications and key features in detail.
www.canon-europe.com
Go down to "File-type," this was also expressed in the other manuals, I don't recall where exactly, but in one of the manuals it was exactly the same as explained here. 12-bit silent shooting, 13-bit in 12 FPS, 14-bit at 8 fps, but still might be useful for my wildlife pics during the day ;-)