Welcome to the Make community!
If you use “Group By” field, you’ll need a second Array Aggregator if you want to Bulk Update Rows.
This is because “Group By” can produce more than one bundle - one for each group.
Hope this helps! Let me know if there are any further questions or issues.
— @samliew
P.S.: Investing some effort into the Make Academy will save you lots of time and frustration using Make.