If the .rar contains multiple files, install the Base Game first, followed by any Updates and then DLC.
The .rar file is a container. Use a tool like or WinRAR to extract the contents.
FUSER's official multiplayer servers were shut down in December 2022, so the single-player campaign and freestyle modes will be the primary functional components.
Use a tool like DBI or Tinfoil on your Switch and a companion app like NS-USBloader on your PC to transfer the file directly over USB. This avoids the 4GB file size limit of FAT32 SD cards.