Thank you all for your replies. First, yes, I converted to Di2 and ran all cables internally so freeing this bolt is not necessary; however, I wanted to know what to do to remove it if I wanted or needed. As the threaded female part is fixed in the frame, I want to be careful not to damage the frame.

I have not yet tried something such as liquid wrench or other penetrating oil. I wanted to be sure I was not doing damage to the frame, whatever method I used.

Bob