Hello and thanks.Welcome.
That silver piece in the very center is not OEM. Someone has some type of adapter stuck in there.
The spindle is clear all the way through so you should be able to get a long screw driver or similar in from the bottom and push it out.
Ohhh I'll try that.What he's saying is you should be able to use some sort of a tool from the bottom and push it up from the bottom. Most likely need to remove the wheel and fender to do so. If you're not worried about destroying it, I'd try and drill it. With some luck, the bit will grab and spin it out. What bike is this? Maybe we can see what OEM looks like.
You are likely correct. On my 2010 a piece of 1/2” copper plumbing pipe was a perfect friction fit for a camera mount I fabbed up.I'm thinking that a long (6-8") 1/2" bolt may drive it out from underneath. This assumes that it's not threaded so you can't pull it out. My K6 1000 has a 13.5 mm hole and I'm assuming that his is the same.