Also reminds me of the maximum amount of coins you can have in runescape: 2.147B. They even created silver coins worth 1000 normal coins as a workaround for people who get to a “max cash stack”.

(Max value in java, even though the game is non longer written in Java)

The language is irrelevant; this is the maximum value of a 32-bit signed integer. Specifically, 2,147,483,647.

Java (and other languages) have other ways of representing numbers which allow larger values, but once you've encoded values into wire protocols and persistent data structures, they tend to be hard to change.

I think OSRS is still all Java, no?

I understand why an 8 bit number would be used for counting...

But that limitation makes no sense for WhatsApp user limit count. Presumably every user has an id number identifying them (maybe a long integer). You need to maintain a list of these users so your array is already way larger than 8 bits.

Can someone intuit why the 256 limit in WhatsApp?