A search in ArcGIS Online finds layers in the current Map Viewer, but not in the Beta.
Hey Kevin, I took a look at the layers you were searching and WMTS layers cannot be added to new maps currently. The Map Viewer Beta currently does not support saving out new maps with WMTS layers added to it so we've restricted the search to just feature layers and tile layers (tiled map services). The app does support reading existing maps with WMTS layers but layer authoring is limited.
Compatibility Guide for web maps created with Map Viewer (classic) and Map Viewer Beta
Retrieving data ...