Click "convert" to open this document..... doesn't do anything!!
The error message then tells you "You are not currently signed in to the
CC (which I already am). Please go to Help- > Sign In and enter your Adobe ID. Restart InDesign, then try opening the document again."
Performing this action does nothing, the error never goes away, you just go in circles.
It looks like InDesign is not recognizing that you are already signed in.
Please try signing out from InDesign once. Quit and relaunch InDesign. Also you could try signing out from Creative Cloud App and sign back in to see if the issue goes away.
Adobe InDesign team