Highlighting duplicate emails across multiple Google Sheet worksheets

I'm trying to extend user0's beneficial formula to more than 3 sheets, but Google Sheets reports an error in the Conditional Formatting custom formula field

From this:

=(COUNTIF(Q:Q,Q:Q)>1)+(REGEXMATCH(Q1,TEXTJOIN("|",1,UNIQUE({INDIRECT("Sheet2!Q2:Q");INDIRECT("Sheet3!Q2:Q")}))))

to this

=(COUNTIF(Q:Q,Q:Q)>1)+(REGEXMATCH(Q1,TEXTJOIN("|",1,UNIQUE({INDIRECT("Sheet2!Q2:Q");INDIRECT("Sheet3!Q2:Q");INDIRECT("Sheet4!Q2:Q")}))))

Any ideas?