See [discussion](https://discourse.julialang.org/t/julia-wont-open-after-updating-macos-julia-can-t-be-opened-because-julia-is-not-allowed/126199/23) on Discourse. There might be a [workaround](https://developer.apple.com/forums/thread/723842?answerId=743165022#743165022). In any case, the download page should warn the user about the issue.