It also assumes that your DHCP range is the top half of the last byte. That's a de facto convention in consumer routers, but not codified anywhere and the kind of thing that could change and probably isn't even correct for some routers shipping today.
Definitely not codified anywhere, and not in any of the routers I’ve used (to be fair they are more prosumer).
The main dhcp server used in most routers, dnsmasq, also assigns IPs using a MAC algorithm by default for consistent IP addressing of devices in a LAN. You would need to explicitly configure it for sequential first come first serve.
Tbf, this is the fault of network people, not the poor support guys left holding the bag of shit. The whole stack is still dangerous and obscure, 25 years after the internet went mainstream. UPnP was an effort at simplifying the situation and seems to have failed, so now we're back trying to teach IT toddlers to spell "characteristic" when they don't even know the ABC (nor do they care about it). It's inevitable that shortcuts will be taken.
> 4. Enter the IP address you found on the network device, but add 20 to the last section of digits, and then select OK.
> As an example, if your computer's IP address displays as 192.168.2.5, enter 192.168.2.25 on the Nintendo Switch.
Hope you don't have more than 20 devices on your network (after your PC), and that they're not configured to be close to 255 there...