Jonah, At Pro v.2.2, elevation settings got moved from the Map properties dialog box to the Contents pane of the scene. If you tried setting the TIN as the elevation surface, it sounds like you know this already. How did you try to set the TIN as the elevation surface?
This is what I did: added a TIN to a scene in Pro. It went under 2D Layers in the Contents pane (same as it did for you). At the bottom of the Contents pane, under Elevation Surfaces, I right-clicked Ground and clicked Add Elevation Source. Then browsed to the TIN dataset location on disk. Now when you identify TIN locations, the elevation units reported in the status bar next to the x,y coordinates should be the values stored in the TIN. (Whereas if you click somewhere off the TIN, elevation values in the status bar reflect the default ground surface: WorldElevation3D/Terrain3D.)
In the Map Properties dialog box for the scene, you might still need to check your elevation units (on the General tab) to make sure the correct reporting units are being used. Like if your TIN elevations are in meters, this setting should also be meters.