The new Mixed Reality feature is now available in Experimental mode! Hence it isn't production ready, however, I highly recommend you start playing with to get familiar with it. In this video I'll walk you through how you can use the Measurements controls to find length and area of an object.
Here is the link to go vote for adding the feature to automatically calculate the area and volume of an object - https://powerusers.microsoft.com/t5/Power-Apps-Ideas/Automatically-calculate-the-Area-and-Volume-of-an-object/idi-p/631085
Here is the link to the Microsoft Docs-
https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/mixed-reality-component-measure-distance
