I was struggling with the same issue the other day.
Solution is pretty simple.
I assume that you have assigned Header partial design to
header placeholder and Footer partial design to
footer placeholder in respective partial designs.
In Page design therefore
footer placeholders are not available anymore.
I believe that in Page design you have assigned Page Content component or something similar to
When these three things are like this, when you are in Experience Editor you won't see "Add here" anymore as all placeholders are "taken".
To enable something in
main placeholder, put there Row splitter component in Page design and move everything that you had in
main placeholder to first row.
Then you will be able to add new content in second row of that splitter.
More information here: