Display issues

Hi there.

This started when I was using my iMac 2013 and is still here after 'upgrading' to my Mac Mini.  When ever I open LrC it opens in full screen mode on both monitors and the only way out of it is either do a force quit or Cmd+Q.  I cannot swap between applications.  It always goes to duel monitor.  I am on LrC 11.3.1.  I have uninstalled and reinstalled it.  It is the only Adobe app that does this.  My Ps and Lr programs run fine.

HAve I checked a box by accident.  HELP