[dvdkhlng]

I think the Linux desktop (at least when running under an xserver) does have an obscure keyboard-mouse function, see e.g. here [1].

This seems to be enabled by default when running the german-centric 'neo' keyboard layout ('setxkbmap de neo'), see here [2]. It is usable on the desktop that I'm typing this from (Devuan GNU/Linux with xfce4 desktop), tested it this moment (no numeric keypad on my keyboard, but with the neo layout Mod4 + right hand keys can be substituted for the numeric keypad)

[1] https://linuxreviews.org/HOWTO_use_the_numeric_keyboard_keys...

[2] https://www.neo-layout.org/Benutzerhandbuch/Tastaturmaus/

[salamandersauce]

Windows and MacOS also have that. I think they both call it mouse keys. It's an accessibility setting.