Just ran into this as well. Like OP I am generally on the mod-facing side & was not super familiar with the user flow for post approval, but just joined another Discourse forum that has post approval enabled and was surprised to see that after the “Your topic is awaiting approval” there’s no way to see it afterwards: it just disappears. Presumably I’ll get some sort of notification when it’s approved (or rejected), but there’s no way to tell for certain since as far as the user is concerned that topic doesn’t exist. It could be that the request didn’t go through because of a spotty internet connection, and I would never know. I trust that it went through successfully (otherwise I should have gotten an error message), but there’s just trust – no evidence.
It would be great for users to be able to see their pending topics in order to have confidence that the feature worked & monitor the status of their topics. Because these aren’t exposed to the user, there’s also no way for the user to withdraw the pending topic like they can with pending posts.