C-Kermit is, to this day, unavailable for apt installation for Ubuntu 20.04.
I got the tar from columbia.edu, tried to compile but failed.
I am unable to adjust brightness levels through Gnome. I had the same issue with 18.04 but it was resolved there (honestly, I can't remember how).
lspci|grep VGA
00:02.0 VGA compatible controller: Intel Corporation Core Processor Integrated Graphics Controller (rev 18)
xrandr --output LVDS-1 --brightness 0.95
<-- this works through the terminal
excerpt from /etc/default/grub
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"
Thank you in advance.