This solution assumes that the values of startdate and enddate are valid numeric SAS date values.
data have;
startdate='03JAN2022'd;
enddate='05MAY2022'd;
run;
data want;
set have;
diff_months=intck('month',startdate,enddate);
do i=0 to diff_months;
if i=0 then newcolumn=startdate;
else if i=diff_months then newcolumn=enddate;
else newcolumn=intnx('month',startdate,i,'e');
output;
end;
drop i diff_months;
format newcolumn date9.;
run;
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