There was a discussion from a year ago that suggested that the Esri Portal Feature Service Reader was updated in FME 2023 build 23210 to resolve domain values when the domain is applied at the subtype level of the featureclass, as it is in the Esri Utility Network.

Esri Utility network reader subtype layer | Community (safe.com)

I am still having trouble getting a domain resolved that is at the subtype level. Maybe I’m doing something wrong?  
 

FME2023.1 (build 23619)

Using the Feature Reader transformer: Portal Feature Service of my UN data, layer is PipelineLine

Looking at the attribute material:

In the schema result from the reader I see 

attribute name: material

attribute name: material_resolved

But in the data result I only see

material: M

and no material_resolved attribute that I can find.

But I can see that other domains resolved, like manufacturecomponent