It was only a matter of time and we will need to do this going forward to support Mac arm64 anyway.
In the tests of my builds, someone responded in 10.9, so it works at least that far back. This fits up with my work experience where the more recent line is around 10.9 or 10.10 due to API changes and deprecations in the OS.
One option is to make the 32 but builds for 10.6 - 10.8 and have the 64 bit build for newer system only.
For Mac arm64 + x86_64 builds (universal2), we need at least a 10.15 system I believe or possibly 11.0 in order to run a new enough Xcode which will support arm64.