If you are looking at a Nintendo Switch with a serial number starting with , the short answer is: Yes, it is definitely patched.
If you want to be 100% certain, you can verify your console’s hardware version using these methods:
These use the improved Tegra X1+ chip. Their serial numbers almost always start with XKJ or XKW . These consoles were built from the ground up to prevent the Recovery Mode (RCM) exploit. How to Confirm Your Model
These typically have serial numbers starting with XAW or XAJ . Only the earliest units are "unpatched" and hackable via software.
Nintendo released two main versions of the standard Switch. Understanding which one you have is the key to knowing if it's "patched":
The XKJ1 prefix indicates that your console is a , which was released with upgraded hardware that permanently fixed the unpatchable "Fusée Gelée" exploit found in early 2017–2018 units. Why XKJ1 Serials are Always Patched