Well I think I resolved my issue. I created a new Solution/App and added all my existing Apps one by one, testing along the way. I made sure that all my existing Apps were ticked as dependencies for the new App that was created along with the new Solution. It now Generates and Builds all my DLL/EXEs as it should.
I think what had gone wrong is that the App that gets created with the Solution was not itself included in the Solution. I don’t know why. I looked at my old computer that has C11 and C10 on it, and the Solution in C11 did not have that App in it, whereas the Solution in C10 did. My assumption is that App needs to be present in the solution, even if it’s just a blank.
I don’t know how or why it got removed, if I did it invertedly or if it somehow happened when I went from C10 to C11. But everything seems to be working as it should now and I am quite relieved.