No way of changing the screen brightness in Ubuntu Studio 20.04 LTS on a acer TravelMate

I finally got my Fn brightness keys working ! Here is how:

1. Reboot
2. Go into BIOS by holding down F2
3. Go to Main tab
4. Change Graphic Mode from Switchable to Discrete
5. Save changes and exit
6. Continue boot
7. et voila !

But … my screen resolution had become low, and everything looked as if someone had trod on it … somewhat squashed …

I was able to fix that, too:

1. Open /etc/default/grub with root privileges in your favorite text editor
2. Change #GRUB_GFXMODE=640x360 to GRUB_GFXMODE=1360x768 (my screen resolution is 1360x768)
3. Run sudo update-grub

Additionally, I ran sudo prime-select intel - I do not know how much that helped. After that, it finally worked.

And, after 1 to 3 reboots (I dont know how much exactly), I finally even got the folders in /sys/class/backlight back ! :)