Can I block a Wi-Fi network from appearing?

Any WiFi network that is within range of your iPad, that has not been configured at source as a hidden network, will appear in the list of “other networks” in iOS/iPadOS WiFi settings.

Your available options to suppress reception of unwanted WiFi Networks SSIDs are limited. You can either move away from the source - or reduce the signal strength below the detection threshold by blocking the signal with a high density or metallic (i.e., signal reflective) screen. While the latter is technical possible, it is perhaps not feasible.

Alternatively, consider a civil and constructive conversation with your neighbour - in which to explain your difficulty and hopefully reach an appropriate accommodation.

You might also explain to your customers that other unwanted WiFi networks, by their very nature, can sometimes appear in Network Lists. With appropriate explanation, most will understand that short of operating in a controlled “radio quiet” test environment, you have no control over networks (and network names) that might be received.

That's one of the tamer examples.

Not in iPadOS. The list of “other networks” will include all broadcasting SSIDs within detection range of your iPad.

That's wonderful!