It's very much up to the nominators, from my point of view, except that I'm unlikely to approve the canonical AO3 fandom tag for it without there being a clear consensus between nominators about the scope of what comes under it (which to be honest seems a bit unlikely).

The split between "Harry Potter - Books 1-7", "Harry Potter - Wizarding World (including Pottermore)" and "Harry Potter - Wizarding World (No Pottermore)" that we've had in the previous two rounds seemed to work well, but it may be that people want to subdivide things further and be clearer about whether they're including (or not) Cursed Child and Fantastic Beasts. I'm very relaxed about fandoms overlapping with each other.