This one should be easy but I cannot figure it out.
I have a Stream Order field with values 1-8. I want to group them like I do in symbology.

But in the charts I see no way to group values for category

So I wrote an Arcade expression in the popup to do it. But the Arcade expression does not show in the chart drop down list for Category for some reason. I do not see it in the attribute table either like I do in AGOL.
How can I do a simple grouping of values? I want it to be dynamic and not be a new field.

Thanks a lot