Remember that I can’t see or “feel” the assembly. Trust your senses over my words.
Looks like either the threaded post on the mount or a threaded insert in the cage has broken loose and is spinning freely. Hopefully that bolt isn’t threaded all the way up into the camera body, in which case that threaded insert, the tripod socket in the camera body, is a potential point of failure - particularly if the connection was overtorqued during installlation or use.
Try putting pressure on the joint by prying apart the two mounting surfaces as you twist as normal. (If you can remove the camera from the cage, do so. You might also be able to push directly down on the post with a punch or small screwdriver.
A small saw, or a rotary tool cut off wheel are both (destructive) options for separating the bits .