[wim]

The lens mount is rather large and if your lens or adapter has a small protrusion, it might hit the shutter as it's much closer to the mount than you think it is. Even some old m39 lenses might be serious offenders.

Also something tells me that if the shutter closes as soon as a lens is removed and only opens back up if the connection is reestablished, it might get tricky to use third party dumb adapters with no electrical contacts.

Come on, obican. I have used Pentax K and M42 lenses on my Canon's, which have extruding parts. Those sit right where yoiu are close to the mirror. Never a problem. Same with M42: do note that I actually use Metabones adapters, which progressively stick further into the "mirrorbox", to a degree that the XL actually just/just not touches the framing screen in front of the shutter. Never a problem.

The same is true for lenses like the old Leica ones. EOS R has the same sensor to flange distance as Leica has - 20 mm. Nobody ever complained about that. And a sensor, BTW, or sensor filter stack, is much more vulnerable than a shutter is, as it is not flexible and/or bendy, and scratches quite easily, unlike the titanium blades of a shutter.

The moment you add an adapter with a non-EOS R lens, it is impossible to insert any part of that combination far enough into the camera that you actually touch the shutter. If that was the case, you could do so with a proper EOS-R lens as well. And it does not matter whether you would attach the adapter first, or the lens plus adapter straight away.

If you do want to get worried about a camera system with that potential, consider the Nikon Z-system. 16 mm flange distance, and a slightly larger mount, plus a zillion lenses that have protruding parts.

Honestly, if there is a person so clumsy they fully stick their paws into a camera and touch shutter or sensor, they shouldn't own a camera with interchangeable lenses. A lens with or without an adapter won't be able to get there, only a finger will, and only if it is done deliberately. And that has always been the case, with any ILC.

Kind regards, Wim