I am troubleshooting a query to publish a web map and feature service in a local coordinate reference system. The reasoning behind this request is that the web map and associated feature services will be used in a WebApp Builder app. The app will be used to add and edit points amongst other things. Within this request, there is a requirement to enable the entering of linear coordinate units using the local CRS and not use the standard lat/long values for 4326 or XY values for 3857 pseudo-mercator projection. There are a few workarounds one of which includes providing guidance on how to convert/transform coordinate values but this is a workaround and not a very good solution given the context of the request.
I have seen that there are base maps and services in AGOL which are projected in CRS's other than 3857 for example the OS Open Carto is projected in British National Grid.
Therefore, after some context, the question is:
What is the full workflow, when using ArcGIS Pro 2.4 to publish a web service to act as a base map to an ArcGIS Enterprise Portal in a projection other than 3857?