Ban related to Animal Crossing New Horizon is definitely not Splatoon 2/3 and Super Smash Bros Ultimate, but it is very unusual, rare and complicated that likely associated with map editor that cause a issue in game or possibly glitch with anti-ban protection in Atmosphere when someone go online with CFW. It cannot be explained completely about whichever is cause.
Ban that associated with Dream is delete your map from Dream server, so nothing is serious like in game ban or console ban plagued in Splatoon and SSBU.
You should have no problem to invite your friends and just ensure that you don't have hacked objects on map and be mindful of run CFW online since ban is very unclear and cannot be explained.