We have 2 different cached/tiled ArcGIS for Server map services, but with different spatial references. One is with the common Web Mercator Aux. spatial reference, the other is an Australia-specific one.
Is it possible to use these 2 together as basemaps in the same web application? I would have the Web Mercator Aux (WKID 102100 or 3857) as the "default" i.e. added to the map first, and the Australia-specific cached map service as the "secondary", so it would project-on-the-fly.
I am using ArcGIS JavaScript API 4.18.
I will be using the default basemap gallery widget, but can implement our own, as I understand the out-of-box basemap gallery widget won't work with different spatial references.