Hey Lynn!
I'm in a similar situation but I've been able to play VR games through ALVR and the Quest 2 without an issue.
For starters, your friend doesn't need a specific USB C cable, he could use a USB C connected to the Quest 3 and a USB A 3.0 connected to the PC.
I take it that he installed ALVR through the AUR, being Garuda an Arch-Linux (I use Arch BTW) distro. I had several issues with that version and I fixed every issue using the alvr_streamer_linux.tar.gz download in the release page, see here for instructions.
Things that should be taken in consideration:
- both the ALVR client (installed on the Quest) and the ALVR server (running on the PC) should be the same version number
- the latest SteamVR patch breaks ALVR, hence it's mandatory to select "previous_version" through the Beta configuration of SteamVR (see here