If the right were getting people fired for perfectly ordinary left-wing opinions supported by a majority of people, that might count as cancel culture. Like "I support single-payer health care" or "ban assault weapons [sic]".

Getting people fired for advocating the assassination of a president, whether it is right or wrong, is not 'cancel culture'. Who here would be surprised or outraged if a company fired someone for publicly advocating the killing of Joe Biden?