I'd consider myself a completionist, but I take it slowly. Personally, I've never finished a world without getting bored. I'm very close to finishing the decoration for my town and I'm working on badges.
I'd say I'm not really a completionist. I do try and complete the museum in all of my animal crossing towns but that is about it. Catalog and nook miles achievements I could never see myself trying to complete. I mainly just focus on what I find fun in the game, which for me is decorating or making money.
I'm not really a completionist as the incentive to actually collecting things in ac is usually nothing. I'll try and complete things here and there if I'm interested in getting it but usually I don't go out of my way to do anything