Or extract LLVM-${ver}-universal.xctoolchain.tar.xz to Toolchains directory: sudo tar -xvf LLVM-12.0.0-universal.xctoolchain.tar.xz -C /Library/Developer/Toolchains ...

The easiest way to use this project is to not use it at all - at least, not directly. Briefcase is a tool that uses this template, rolling it out using data extracted from a pyproject.toml ...