Not sure why you think its unproven, it's actually one of the supplements used in weight sports that has possibly the largest amount of solid evidence behind it.
Frankly that seems a little strange to me. Was it not known as one of the most commonly used supplements in weight lifting for a long time before it was thought of as a nootropic? Just googling creatine gives all sorts of results about it being a sport supplement
Honestly, I don't know. I'm not into nootropics, just a random "fact" I was aware of (fact being this group considers it a nootropic lol). But I'll reference the reddit guide if you want to dig in yourself[0]. But I'm not sure I would expect a great answer as these types of subreddits often have an abundance of unwarranted confidence.