Well, it depends on how you define fanfiction. Technically, Dragon Ball Super is an official continuation of the Dragon Ball series. However, it does have elements that feel like fanfiction. For example, some of the power - levels and new forms introduced seem a bit outlandish and more like what a passionate fan might come up with rather than a strictly logical progression from the original story. But it's still an official part of the franchise so it's a bit of a gray area.
Yes, 'Dragon Ball Super' fanfic is quite popular. There are a large number of fans around the world who are passionate about the 'Dragon Ball' universe. Fanfic allows them to explore different storylines, character developments, and scenarios that may not be part of the official canon. It gives fans the creative freedom to expand on the existing world, whether it's creating new power - ups for the characters, exploring different relationships, or imagining entirely new adventures.