Given the information:
Using a “New” XCI file downloaded from the internet is only technically legitimate if you own the original cartridge and are using the downloaded file as a backup for preservation purposes (e.g., your cartridge broke, or you want to play without swapping carts).
Once installed, your Switch home menu will show the Serious Sam Collection icon. Press + on the icon. Go to “Software Information” -> “Version.” A “New” dump should show version 1.0.1 or higher. If it shows 1.0.0 , you have an old, unpatched release that may have performance issues.