This article (June 2018) says that feature layers participating in view layers with joins can't have their schema altered.
Is this information still valid?
We've been experiencing this with a hosted feature layer which may need to have changes to some field domains (from the Data tab in the item details page). This means we'll have to delete and recreate the view and the web map each time users ask for a change in a domain. And some extra steps to make apps use the new web map.
The weird thing is that in a test feature layer we were able to change field names and domains in AGOL after creating a view with it using the Join Features tool. I've been unable of reproducing this again but it makes me think there's an exception to this limitation. Am I right?
ENH-000142669 : Provide the ability to be able to add/edit fields in for a hosted feature layer after running the "Join Features" tool in ArcGIS Online https://my.esri.com/#/support/bugs/ENH-000142669
BUG-000119730 : In ArcGIS Online, after running the Join Features tool on a layer and a table within the same hosted feature layer, the Add Field option for the hosted feature layer disappears. https://my.esri.com/#/support/bugs/BUG-000119730
Hi @MundellEarth you can create an idea in Esri Community and get votes for our teams to give a look at those development enhancements. Or you can also create a case with tech support to review if is there any enhancements logged under the same idea.
I had a similar experience where I could, for a brief time, make schema changes to a HFL after creating a join. I think it was just a matter of the change in settings to catch up with the AGO server. The ability to make schema changes on that HFL went away after an hour or less.