Run using the latest version of python installed via homebrew. The OS version is often too old. Look for an error like "macOS 26 (2602) or later required, have instead 16 (1602) !".

brew install python3
brew install python-tk
brew install tcl-tk

/opt/homebrew/bin/python3 -m venv ./my-guizero-script-dir

source ./my-guizero-script-dir/bin/activate
cd ./my-guizero-script-dir

If moving from an old python venv with native python:

Old venv:

source old_env/bin/activate
pip freeze > requirements.txt
deactivate

If transferring requirements via requirements.txt from a native python venv make sure to update constraints from == to >= or package versions may be too old to run in latest python.

New venv:

/opt/homebrew/bin/python3 -m venv new_env
source new_env/bin/activate
# update requirements.txt with >= to allow later versions
pip install -r requirements.txt