Loved one uses toilet on own, but feels he must remove poop from bowl to throw away. Always trying to hide it from us. Suggestions?

A self flushing toilet that the moment he stands up to reach into the toilet, it automatically flushes.

Your loved one obviously has some form of dementia, and should no longer be allowed to be in the bathroom by himself.
So going forward make sure that someone assists him when he goes in to use the bathroom. It's actually quite a simple solution to this problem, don't you think?
Don't try to make this harder than it has to be.

If you think allowing him to use the bathroom unaided is preserving his dignity think again, there is nothing dignified about what he is doing or your allowing it.

I agree with Geaton. He now needs to be accompanied to the toilet. You are in the latter stages of dementia when this sort of behavior happens. He won't be capable of understanding anything regarding this and will have to have someone with him.

What would you consider a solution?

Obviously he cannot understand what he's doing and therefore cannot use the bathroom unassisted anymore. His aid would need to flush the toilet immediately after his BM to prevent him from doing that behavior.