Typically found on archival, homebrew, or ROM sites (like Ziperto), where community members share copies of eShop games [5.5].
If you are looking for information on installing a file you already own, I can provide steps on using [5.4]. RECALL Switch NSP (eShop)
It is the standard format for digital games and DLC downloaded from the Nintendo eShop [5.5]. Typically found on archival, homebrew, or ROM sites