Cannot symbolize by Predominant Category when using custom expressions

[AustinCanty1]

I'm trying to display three values using the Predominant Category style. This works fine when I add my first two attributes, but when I add the third from a custom expression, the predominant category drawing style choice is removed.

CC  Mike Minami‌

[MikeMinami]

Unfortunately, the predominant style doesn't support Arcade expressions as input.

Change style—ArcGIS Online Help | Documentation 

Arcade expressions are supported for all styles except Heat map, Predominant Category, Predominant Category and Size, and the Age styles.

thanks,

Mike