What is this annoying popup when I try to edit text:

Solution 1:

This appears to be coming from the productivity app Things 3. You may have this in your login items (Settings → Users & 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/