first of all version 17.3 is very old - I suggest to upgrade to September 2019.
make sure your designer and server are on the same version
the fact that connections are greyed out is normal, what surprises me is that normally you should see there entities like
Page
Levels
Images
Tables
Cells
Variables
Formulas
Once you right click on one of them you should see Ädd object"and then you should be able to pick an object associated with Application and connection you want.
Without more info i don't know what else I can suggest. It simply looks like corrupted designer or not configured properly.
Are you able to edit any other reports?
cheers Lech, When applicable please mark the correct/appropriate replies as "solution" (you can mark up to 3 "solutions". Please LIKE threads if the provided solution is helpful to the problem.