This is an old thread! Try:
=LET(aDate,G4,dom,WORKDAY.INTL(EOMONTH(aDate,-1),SEQUENCE(15),"1010101"),FILTER(dom, MONTH(dom)=MONTH(aDate)))
where aDate (cell G4 in the formula above) is any date in the requisite month
or convert it to a named lambda with:
=LAMBDA(aDate,LET(dom,WORKDAY.INTL(EOMONTH(aDate,-1),SEQUENCE(15),"1010101"),FILTER(dom, MONTH(dom)=MONTH(aDate))))
So that you can use it (with argument hints) thus: