Searching for "Mario Kart 8 Deluxe Switch NSP XCI Update 30 Exclusive" will lead you to ROM sites and torrents. Be aware:

In practical terms:

It sounds like you’re looking for a about finding Mario Kart 8 Deluxe for the Nintendo Switch, specifically involving the NSP/XCI formats , update 3.0 , and perhaps some exclusive content.

When managing software backups for your Nintendo Switch, you will primarily encounter two file extensions: NSP and XCI. While they achieve the same result—loading your game—they originate from different sources.