Hi @madisd,
thanks for reaching out!
So, after a quick search on the forum, it lokks like your issue is not new. [Here]{Problem running root on macOS 10.13.6: ERROR in cling::CIFactory::createCI(): cannot extract standard library include paths!} the problem was solve by reinstalling ROOT from source instead of using brew.
BTW, can you tell what’s the output of clang++ -xc++ -E -v /dev/null 2>&1 | sed -n -e ‘/^.include/,${’ -e ‘/^ /.*++/p’ -e ‘}’?
Cheers,
Monica