Arc support was added after release to Linux Kernel 6.2 and it’s steadily improved since. Older Linux distros, or “LTS” oriented distros that favour stability may still not have support for them. I know Unraid was very slow to pick up on it and I had to settle for passing the pcie device through to a VM to get it working. Intel is keen to made these viable though, and I love having the AV1 encoder from my A380.
Flatpaks are basically containers, allowing applications to maintain their own dependencies separate from your system. It’s similar to a Windows program shipping with its own precompiled DLLs, helping prevent dependenct conflicts when you go to update something you installed with pacman or yay.