What is this annoying popup when I try to edit text:
This appears to be coming from the productivity app Things 3.  You may have this in your login items (Settings → Users &amp; Groups → User → Login Items).  Disable it there to prevent it from automatically starting.

Their support site has a great deal of info on how to use the product, but I was unable to find anything on preferences/settings.  There should be something in their settings that enables/disables actions when you select text.  

If you have further difficulty, you may wish to contact that developer directly through their website: https://culturedcode.com/things/support/