I have a mid 2011 iMac that could become my openHAB server since it is currently just gathering dust. What operating system would be best to run openHAB - either macOS (El Capitan) or I could convert it to Linux. Am I likely to run into unexpected issues either way?
just my personal assumption, but I think most people run it on raspberry pi, which means Linux. not sure if the foundation is tracking any usage data.
you can run it on your Mac.
I tested it on my Mac. and then installed on my server
check the link to see.