Yes, the camera fits in. However, the operation is not possible without restrictions.

Yes, the Canon EOS R fits in without any problems (as long as there is no telephoto lens on it). It is also waterproof. The only problem I had was that at a depth of about 13 metres, the camera is virtually vacuum-packed because the water pressure is so high. As a result, my shutter button remained pressed in and I couldn't take any more photos. This problem is solved by diving a little upwards. Otherwise, it serves its purpose, but is rather cumbersome to use.

Yes. The camera will fit in without any problem, but it won't be a perfect fit. It's more like the camera is in a plastic bag.

The case, actually a plastic bag, is bigger than the camera, I use a Sony A7. It's a bit wobbly until you squeeze the air out and close the bag. I stabilised it with two small cloths. It should also be noted that the water pressure pushes the zoom into the rest position, so in my case from wide angle to 50 mm. So a fixed focal length would be better.