How to change which widget is displayed on multi-function devices?

Unfortunately this feature disappeared when they moved to the new tile layout. See the below thread for custom code for things like the multi that will switch what the main sensor is.

Note that using the custom code will move the device to running in the cloud as opposed to local with a v2 hub.

Another option is to search around for a SmartApp/device-type that let you pool multiple sensors into one view. I know there was one for battery levels called battery monitor, but I can’t find the threads right now.