Why are my PC action keys/ hotkeys/ multimedia keys on the fn keys NOT WORKING?

About a week ago the keyboard function keys that I use to mute/volume control/ brightness/airplane mode etc on my HP Laptop just stopped working. I assumed my toddler had mashed some combination of keys that has toggled off this functionality - the 'mute' light still works when I mute it via the Volume/sound settings, and the fn keys still do their functions, but nothing I've tried has gotten them to work again.
I've gone in the BIOS and checked that Action Keys are enabled.
I've checked for new drivers (keyboard and HP Utility keys) but nothing seems to be needed or does anything if I install new ones.
I've done most of the things listed here https://tencomputer.com/fix-volume-keys-not-working-on-windows-10/ (for Solution 5, I don't get any of the 'customised' things shown in the screenshot, so no 'Function Key Row' dropdown).

Some google potential answers are just ways to lock either holding or not holding the fn button while pressing the f6 key or whatever to get it to do the 'action key' thing but holding fn does nothing.

Any ideas please?
I'm posting this in the superstitious hope that the next thing I try will work and I can post back 'n/m, sorted'

if nothing else you could use a program like KeyTweak and try to manually set the keys to what they're supposed to do

and if that doesn't work, you can set other keys you don't use to have the functions you need... i moved my volume settings to the RAlt, RCtrl and menu keys because i didn't like them in action keys