We were able to reproduce your issue on one of our Mac laptops. If we are indeed experiencing the same issue, it was due to a recent VTK update.
We have just made a patch release that should resolve this.
Could you please download the latest version of QTCAD (now 1.3.2) on our client portal?
Then, we would recommend the following steps:
conda env remove --name qtcad
conda env update -f qtcad-mac.yml
conda activate qtcad
pip install .
Could you please kindly let us know if this resolves your problem?