outdated

If you do brew tap omnisharp/omnisharp-roslyn you get version 1.35.3.
The current version of omnisharp-roslyn is 1.37.17.

also, it simply does not run. is this just completely abandoned?

[VimalMollyn]

To make it run, I had to modify the executable script created by homebrew to use the correct base path for homebrew (/opt/homebrew for me on my M1 mac).

#!/usr/bin/env sh
mono /opt/homebrew/opt/omnisharp-mono/libexec/OmniSharp.exe $@