What are canonical penalties for criticizing the Pope?

I was listening to *Pints With Aquinas* this evening where Dr. Richard DeClue, a professional theologian, not a priest, was interviewed, but he didn't want to comment on some _motu proprio_ (probably [_Traditionis Custodes_](https://www.vatican.va/content/francesco/en/motu_proprio/documents/20210716-motu-proprio-traditionis-custodes.html)) citing there were "canonical penalties" for doing so. What is a "canonical penalty"? Does it affect the laity or more the priests and religious? And what exactly constitutes an act that requires someone to be canonically penalized?