I have an Arcade expression that generates counts of features within polygons and I would like to symbolise those values. Because these values do not exist as fields is it possible to build an expression?
The expression that works in my pop-up does not work in 'Change style' therefore cannot symbolise?
I read this post and implies to me it is not possible?
That's correct, it is not possible. The symbology profile of Arcade does not have access to anything but the individual feature being symbolized, so you can't even get information about the rest of the layer, much less other layers.