How many computers in 2025 allow you to use your external USB keyboard numpad as arrows? Not an Apple, at least not without convoluted system-level configurations or third-party software. Apple gets many things right but can still be infuriating on the simple stuff.
Why would you expect it to do that? There is nothing on the keys to suggest they should have that feature and the actual arrow keys are about 5cm away.
Not sure how it is in Mac world, but in PC world the numeric keys have arrows (8 is up, 2 is down, 4 left, 6 right), and you can activate them by pressing NumLock. It has been this way since at least 90s. Never used them myself, but I guess if you are used to them and they no longer work it can be infuriating. E.g. like VSCode removing Insert key functionality (always inserts, never overrides the text).
There are no arrow on the numeric island an Apple keyboard, nor is there a numlock key. There is a 'clear' key on the numeric island in the location where a PC would have a numlock key (it has the function of the 'AC' key on a calculator and functions as such in the calculator app).
I am typing this on a 1987 Apple keyboard on a PC and this numpad functionality works. What I don't know is, is it because of Windows, or because of the ADB to USB adapter?
The numpad keys do have their own scan codes separate from that of the main rows.
Back in 1987, Apple sold a PC compatibility card, and the Extended Keyboard was designed to work with that. So I assume it always sent the correct scan codes.