perhaps someone can advise. See I have a previous version of ROOT install and it worked on MacOS 12.1 until I updated XCode. So is there a way to just use that build if I just reverted back to the older version of XCode?
Which version of ROOT are you trying to install ? I have the master branch and 6,.26 branch working on 12.1 and latest XCode. You need to make sure you start with a clean build and using system libraries. Otherwise you can also use binary builds nightly from Index of /download/nightly
it was the latest version, from source. I tried several things and none worked (source, brew, latest binary) and none worked. I have XCode 13 (since 13.1 didnt work and one of the other threads suggested switching back) and MacOS12.1. I’d rather have it from source since I want to use minuit2 but its not essential, I can find another machine to work on if I need to use that. In the end I was able to get this version to work: https://root.cern/download/root_v6.24.06.macos-10.15-x86_64-clang120.pkg . I’m not sure why it worked and others didnt though.