Quick follow-up, because tonight I installed EndeavourOS on my Surface Pro 4. (It's not Garuda, but it's still Arch.)
If you can follow instructions and copy/paste Pacman commands, you can install the Surface kernel. I did hit a couple of unexpected errors along the way, but the error messages were very specific. So it was easy to resolve them.
The instructions page is written very well, and there's a whole section dedicated to Arch.
There are only two things I haven't done yet: set up secure boot, and enable Bluetooth. Both of those things are pretty well documented, I just haven't tried to do it yet.
You add the new kernel's repository to your repo list. During updates, Pacman will pull what it needs from the various repos.
That's the short-short version. Possibly not technically accurate, but that's basically what it does.
After I ran the setup commands, edited the config file, then ran the command to install + update, it updated without me having to manually select any files.
Be patient and learn, so eventually you have a working system.
Don't have a working system.
The Surface Pro is a very proprietary device. It requires the extra work in order for Linux to function on it.
There are communities of people who will be happy to help you on your journey to learn, but unless you go through the effort you won't solve your problem.