Define the Quantity column to show Actual value; add a hidden multi-scenario column, QuantityDelta, to show Difference; then define conditional formatting for the Quantity column when their QuantityDelta field is not 0.

Define the Quantity column to show Actual value, and define an additional hidden column, Quantity0, as !Quantity#0 using "Calculate using grouped results in the previous row or other results"; then define conditional formatting where the Quantity column is not equal to Quantity0.

Add a hidden multi-scenario column, RecordID, as show Differences; then define conditional formatting for the Quantity column where RecordID is not equal to 0.

Define the Quantity column to show Difference, select the scenario comparison filtering option to show Only records with different comparison values, then define conditional formatting for the Quantity column when the respective value is not equal to 0.