I don't know the answer (I don't care about numlock myself), but the arch wiki has an article on this: https://wiki.archlinux.org/title/Activating_numlock_on_bootup

Perhaps that will be useful to you. In general checking the arch wiki is a good idea for any Linux issues, even if you don't run arch, many things still apply to other distros and the articles are of very high quality.

In this case, "Early bootup (mkinitcpio)" would likely not apply to most other distros that aren't based on Arch, but the rest looks to apply widly.

It is worth noting that in the KDE section it mentions the need to apply two settings, perhaps that could be it?