While searching for is common for backup purposes and emulation, always ensure you are sourcing files safely. Use ad-blockers and verified community sources to avoid malware. Remember that the best way to support the developers and ensure future Strikers titles is to purchase the official game from the Nintendo eShop or a retail store.
It sounds like you're looking for the XCI file (a Nintendo Switch cartridge dump format). mario strikers xci
An online mode where up to 20 players can join a club and compete for points to climb the seasonal rankings. Understanding the XCI Format While searching for is common for backup purposes