I am running ArcMap 10.6.1 and I can not select, edit or move text boxes I have add to my map in layout view. I have several annotation labels in my map all of those I can select, edit and move. Is there something I am missing with the text boxes?
Easiest way to solve this kind of problem is, Close your ArcMap and ArcCatalog and go to your profile
Users > user_name > AppData > Roaming > ESRI > Desktop > ArcCatalog/ArcMap
. Rename existing folder then re-open the ArcMAP and catalog.
This will restore default settings of your ArcMAP and ArcCatalog and all the problems should go away.