As far as I know, there are two layouts. An alphanumeric keyboard if you use an alphanumeric passcode, or a number-only pad if your passcode consists only of digits.
An arbitrary-length passcode keypad differs from the standard 4- and 6-digit codes only in the fact that you have to tap “OK” after you’ve entered all the digits (so a thief won’t be shown the number of digits on the entry screen).
Yes, but sometimes a throwaway account becomes relevant in the future.
Once upon a time, I reused a single password on every web site that I didn’t care about. Until that password appeared on Have I Been Pwned, and I realized that although nobody with this password could financially hurt me, they could post messages as me on any of a hundred different discussion forums. It took me several days to track down and change every one of those passwords (this time to one unique for each site).
These use-cases are simply designed to block people who didn’t actually enter the shop, where they probably can see the passcode printed on a sign. High security is not a concern - they just want to block the opportunists, like people in the shop next-door that doesn’t have Wi-Fi.
Much like hotel Wi-Fi, where the passcode is typically just the name of the hotel with a couple of numeric digits that never change, or something else that everybody who has ever stayed there knows. Again, because the goal is to just block the opportunists, not to actually secure the network.