rc.local sounds like an OpenRC specific thing. We don’t have that, we use systemd. So if the software relies on that, you are out of luck.
/etc/modules is now /etc/modules.d/, again the reason is systemd.
The script looks like it’s just designed for Raspian/Raspberry Pi OS. It also looks to be running the build commands (make and cmake) with sudo, which you should never do.
You might be better off by creating yourself an Arch script loosely based on that script. It’s clear that the maintainer does not actually run Arch and have likely not tried the script on Arch.