Years ago, when I used Linux more, I used to customize the kernel for the particular hardware on a particular computer. I used the Slackware distro which was designed for that kind of thing. It made a very noticeable difference in performance. (Of course that was in the Steam-age when a blazing hot CPU might run at 4.7 mHz.)

I could try to do this from scratch but I am not sure if these newer distros will like it.

Ubuntu seems to have packages designed to do just that. While I believe that neon is based (heavily?) on Ubuntu, I am not quite sure what the relationship is.

Has anyone tried to customize a kernel? What is the package relationship with Ubuntu?

Thank you

Neon is quite literally Ubuntu (just wit a different set of Plasma and KDE stuff), particularly in this regard, so any instructions or tools for Ubuntu 20.04 will be used in the exact same way here.

Ubuntu's generic, unmodified "mainline' kernels can also be used, or other Ubuntu 20.04 custom kernels (Xanmod, etc)
It has been a dog's age since I compiled a kernel myself, it seemed to have little improvement over stock for me and my setup back then.