It seems that you’re not the only one with problems with whatever Julia is being shipped by Arch: Clean Julia 1.0 install on Arch Linux -- Can't add packages - #11 by crbinz
You could try following the steps in that post (touching ~/.julia/environments/v1.4/Project.toml and ~/.julia/environments/v1.4/Manifest.toml` ) or you could try using the generic linux binaries from Download Julia .
Using the generic linux binaries has consistently been the best approach in my experience, although I’m not on Arch so I can’t speak to that specifically.