It looks like Topographic with Hillshade with their own data on top as an overlay. If you're looking for a more muted basemap and one of the existing ones is close to what you're trying to do, you can try to use the Vector Tile Style Editor https://www.arcgis.com/apps/vtseditor/en/. If you haven't used it before, you can use it to modify colors, styles, and labels. We use this often because we like the light gray basemap, but the neighborhood labels will conflict with our own project area labels. Using the style editor, we can remove Esri's neighborhood labels, but keep labels for streets and use the rest of the basemap. Hope this helps!
