I have a point feature service in AGOL that I want to show as active or inactive based on whether or not there is a date value. When features are created the values are null. Essentially I want to show null as one color and not null as another. I was able to accomplish this by using Types (Unique Symbol) based on a Custom Expression using IsEmpty(). It works in my AGOL web map, but not in Collector. There is no point symbology in Collector. I can add a new point, but it doesn't display. I assume this isn't supported, but why? Is there another way to go about this? Is there a way to determine what can be done in AGOL that isn't supported in Collector or Explorer?
As far as I know (symbol) expressions are not supported in Collector. You could try to overcome this if you set up a domain/subtype in your GDB for the field you need different symbols for. Then re-publish it to AGOL and when you set up your symbology based on that field it should pick up the values you just set in the GDB version.
I hope this helps.