Bad experience with logitech k480 keyboard on mac

So I have this trusted k480 keyboard since 7 years.
I have to use it with my windows laptop at school because hp keyboard are trash.
Some bugs I've learned to work around, overall a very good keyboard.
But today I was like instead of moving physically 10cm to the left to reach out for my mac, why not juste use the same keyboard?
I connected it to the mac, installed the old version of logi option which is surprisingly more accessible on mac than on windows to make f1-f12 act as standard function keys.
Everything is almost okay but for one frustrating thing.
For a reason only logitech could know, the fn / globe key, when in the standard mac configuration, act as shift+option combo, and for whatever reason the usual fn + up = page up / fn + down = page down is somehow converted to brightness up and down, and fn left / right arrow doesn't doo anything I am aware of... TLDR to get the sane behaviour for the function key I have to press the left button on the right above the function keys on this keyboard, the ones we generally use to pair a new device with the k480, but then everything switches to windows mode, meaning that I lose both the right command key and my option command keys are flipped like it happens in windows vm or using generic keyboards.
Is there any way to fix this mess?
The firmware is up to date in logi option and there is no other option I can see there to fix this behaviour.
I have not found anything built-in in system settings --> this specific keyboard either, the toggle between media / function key is systemwide but it only affects my macbook real keyboard, not this logitech one.
Any help would be appreciated.