How to sum column based on distinct values from another

Hi , GinjaNinja29 

You may need to create calculated columns as below:

Count 1 = CALCULATE(COUNT('Original Table'[ID]),ALLEXCEPT('Original Table','Original Table'[ID]))

Quantity1 = IF('Original Table'[Count 1]>1,'Original Table'[Quantity],BLANK())

The result will show as below:

You also can try to create measure like this:

Quantity 2 = 
var a= COUNT('Original Table'[ID])
return IF(a>1,CALCULATE(SUM('Original Table'[Quantity])),BLANK())

In table visual , make sure the  fileld "id" show items with no data

Here is a sample.

pbix attached 

Best Regards,
Community Support Team _ Eason
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