Have you ever wanted to know the following:

• Total count of device IDs used per day
• Number of devices that a user is using / count of devices grouped by User ID

If so, Amplitude does support a metric called PROPCOUNT in which returns the number of distinct property values for the property the event is grouped by: https://help.amplitude.com/hc/en-us/articles/115001163231#h_46d7c586-591a-4454-989e-74deab6a732f

You can use this custom formula on an Event Segmentation chart to get the total count of device IDs per day: https://analytics.amplitude.com/demo/chart/gqyzg77

And then add a second event group by UserID to get a total count of device IDs per user per day: https://analytics.amplitude.com/demo/chart/848sph6

Please note that the Event Segmentation chart is subject to the dates in the date picker. So you will only be able to see the count of devices each User ID used during the time period selected.