Assume that you have multiple monitors that are set to nondefault DPIs. When you try to share the non-primary monitor, you can only see two options that are primary monitor and desktop in the application picker. This issue occurs in Microsoft Skype for Business 2015 (Lync 2013).
To fix this issue, install the January 3, 2017, update (KB3141468) for Skype for Business.
Note Lync 2013 was upgraded to Skype for Business in April 2015.