The .rar file you mentioned typically contains a .nsp file, which is a package format used by the Nintendo Switch. It is important to note:
: Enhancing general system stability for a better user experience. Super.Mario.Maker.2.v3.0.2.NSP.Update.rar
: To use these files, a console is usually running custom firmware (CFW). press the + Button
: Highlight the game icon on your HOME Menu, press the + Button , select Software Update , and then Via the Internet . Regarding NSP/RAR Files select Software Update