I recently did some work on a codebase I last touched 4 years ago.
I didn't remember every line but I still had a very good grasp of how and why it's put together.
(edit: and no, I don't have some extra good memory)
I definitely understand my own code better than what other people wrote, even from 10 years ago. I often see code and think "this makes sense to do it this way". Turns out I wrote it years ago.
I find this to be the case if it was something I was deeply involved with.
Other times, I can make a small change to something that doesn't require much time, and once it's tested and committed, I quickly lose any memory of even having done it.
Lucky you. I always go "huh, so I wrote this?". And this was in the pre-AI era.