git clone https://github.com/amaxwell/tlutility cd tlutility git submodule update --init --recursive
to pull the necessary submodules.
Open TeX Live Utility.xcodeproj and set the scheme to TeX Live Utility (Debug) or Release. It should build on Mac OS X Mojave and later.
You will have to create a code signing certificate named “TeX Live Utility Signing Certificate.” This is easily done using Keychain Access, or you can hack the build process to use your own certificate. Note that signing is done in a shell script build phase, since Xcode’s signing was broken when I started developing the program.