As a note, this is a problem with HDF5’s environment detection strategies. It does try_run kind of things to extract out information from the environment. But I guess you’re cross compiling here and not actually on an arm64 machine. I’m actually rather surprised that the former worked and the latter did not (though maybe you’re on an x86_64 host which masks the arm64 problem). This kind of gathering is completely broken for cross-compilation (you can’t generally run the binary) and multi-arch builds because running it only answers the question for one of the targets.