And, if I attempt to package on Big Sur (or inside an docker container running ubuntu) with

platforms=["macosx_10_15_x86_64-cp39-cp39"]

added to the build target, the package command fails with:

ERROR: Could not find a version that satisfies the requirement wrapt<2,>=1.10 (from deprecated)
ERROR: No matching distribution found for wrapt<2,>=1.10