PyQt 6.5.0 does not run on macOS 10.15, despite its wheel name on PyPI suggesting that it should:

• PyQt6-6.5.0-cp37-abi3-macosx_10_14_universal2.whl

The PyQt6-Qt6 wheel for x86 also suggests it should work:

• PyQt6_Qt6-6.5.0-py3-none-macosx_10_14_x86_64.whl

What tripped me, however, was that I had PyQt6 pinned to 6.4.2, but did not have PyQt6-Qt6 pinned. This caused PyQt6-Qt6 6.5.0 to be installed, so then PyQt6 6.4.2 also does not work on macOS 10.15, despite it doing so less than a month ago (before PyQt6-Qt6 6.5.0 was released).

Perhaps this is all to be expected, but I could not find release notes stating that support for macOS < 11 was dropped, and, like I said, the wheel names suggest otherwise.