How to update my just my kernel version on Ubuntu 20.04?

you can try a mainline kernel. Search for how to install them. Or

sudo add-apt-repository ppa:cappelikan/ppa -y
sudo apt update
sudo apt install mainline -y

To install the mainline kernel installer.

You could also upgrade to the latest oem kernel

sudo apt install linux-oem-20.04b -y

Either solution will get you a newer kernel and retain 20.04LTS

I found installing the brightness controller worked. First installed linux-image-5.14.0-1011-oem and the headers but before I rebooted I installed the brightness controller via:

sudo add-apt-repository ppa:apandada1/brightness-controller
sudo update
sudo apt install brightness-controller

Dimming the brightness without dimming the RGB worked to stop the flickering.