SageMath-9.0.app fails to start on macOS 10.14.6

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Happy New Year

Hi,

SageMath-9.0.app fails to start on macOS 10.14.6 :

• the file:///Applications/SageMath-9.0.app/Contents/Resources/loading-page.html appears on Firefox
• the log file says :
  /Applications/SageMath-9.0.app/Contents/Resources/sage/src/bin/sage: line 617: exec: python3: not found

However, everything works fine in a term window

• /Applications/SageMath-9.0.app/Contents/Resources/sage/sage --notebook=jupyter

• copy and paste one of these URLs: http://localhost:8888/?token=688ebf86...

Can anyone help ?

Thank you