First make sure you are using an updated version of AC10. The initial version had a bug.
Second make sure your background fill is transparent or white.
Third go to Model View Option Combinations/Options for Fills & Zones/Fill Background-Change to By Element Settings
Be sure to save this setting in your model view combinations or it will revert.
The percentage fills should now work properly.
Mac OS12.6 AC26 USA Silicon
M1 Macbook Pro