If you’re getting downvoted it’s probably because you sound a bit condescending.
Anyway, most of your issues are Ubuntu issues, not Linux issues. And as you may have learned, most Linux users don’t really go with Ubuntu anymore as a recommendation. Personally, I use Fedora with as many flatpaks as possible and have a great experience.
Clicking on a deb (or .rpm) to install something is a last resort imo. Install from the package manager first, flatpak or snap next.
Variable refresh rates aren’t something I care about so I don’t know 🤷🏻♂️ but sounds very firmware/hardware dependent. HDR is just not implemented fully yet, but being heavily worked on. Linux is in the middle of the final push to switch X to Wayland which will likely fix these kinds of issues once fully adopted.