None of these worked for me. I'm on a mac using Microsoft 360. I found this which DID work: This workaround is for Excel 2010 and 2007, it is best for a small number of chart data points.
Click twice on a label to select it. Click in formula bar. Type = Use your mouse to click on a cell that contains the value you want to use. The formula bar changes to perhaps =Sheet1!$D$3
Repeat step 1 to 5 with remaining data labels.
Simple