The Aggregation formula is as follows: IF(OR(AVERAGE(values), AVERAGE(values)=0), AVERAGE(values))
By wrapping it in an IF statement, you can run various checks. This formula checks if AVERAGE(values) is truthy or it is equal to 0. If you did not check if it equaled 0, the cell would be blank instead of 0 when the average was exactly 0. By not specifying something else to return if false, it will simply return blank.
I didn’t use a rollup field, just because the number is not ALL that is in that table, and it never works right. BUT I was able to switch out where you put (Values) and put the field reference for the lookup field and it works perfectly! Thank you so much!