Lots of posts to answer to here, but we’ll get the arrow icon “clickable” in the next update. The entire rest of the grey area is clickable, appears to have been an oversight on the href for that icon.
Tiy can definitely upload your own 3D models, in the original 3D release there was a bug in that the GLB extension was not in the list of files in the native system dialog that was brought up. You could just drag and drop to the editing canvas itself or to the grey area to add your own GLB fies. That has been fixed, and you can now use all three methods to add your own 3D objects.
When adding an object from the media library, CenarioVR brings up the propert dialog so you can name it, add actions etc. Its not prompting you to replace it at that point.
CenarioVR allows both 3D and 2D objects as hotspots, which is why you can choose JPGs, PNGs, SVGs, or GLBs for you resource type to go aong with a hotspot.