Add values/classes to symbology that are not yet present in the layer
I sometimes make web apps that are used for editing purposes by others. Ideally, I'd be able to add a separate symbology category for several expected values that they'll be putting in, but am not finding any options to do so unless those records already exist. I'm only able to use the 'other' setting. I suppose I could add some dummy data, but I'd really prefer not to as that can throw other things off.
As a workaround, I've found that you can trick it into adding extra values by adding dummy data, deleting the expression, re-entering the expression, re-configuring your symbology, and removing the dummy data. The value classes seem to stay even when the dummy data is gone.
You can now add values to the list of types. These values you are adding wont exist in the dataset yet but once added they will use the configured symbology. The added values do not get added to the types/templates of the layer and are ONLY used for layer styling.
Opening the Types smart mapping panel you will see this new '+' button
Clicking that will open this modal where you set the stored value and display value. The display will autogenerate to the stored but you can edit that.
Then it will appear at the bottom of the list above the 'Other' section
Dragging the newly added value into the 'Other' section will remove it from the list entirely if no features contain that value.