This message about the unavailability of the Unix socket for Incus, means that the Incus service just has not started yet.
I do not know who makes the packaging for Incus on Manjaro. I did not find an entry on the Incus website for Manjaro. Can you point to Manjaro website that talks about this Incus package?
As @qkiel writes, you can start the service manually and continue working on this. If the packaging does not enable the service upon installation, you can enable it.
But let’s figure out the source of the issue so that it gets fixed for all Manjaro users.