My button never popped. It got shallow, but never actually popped out.
Mine stretched out at the beginning, got shallow, then around the top it started bulging out. Sounds just like what you're describing. The skin is super soft there.
Mine was deep also it now looks like it will pop but its not out yet sometimes if my baby sits low it will pop out but then go back in
With all 3 of my pregnancies my belly button has never poped but it was soft n im not a big person.
I'm 25 weeks now and had a very deep belly button as well. It hasn't popped completely out yet, but it has definitely started to shallow out quite a bit. We'll see as time goes on. Lol I started playing with it too so I know what you mean when you said it looks like a small hernia.