Now I will admit, I'm not the biggest user of the PC Editor. At most, I only use it to find out about the hidden sections on various routes, but this is still important as I've had issues with it ever since TSW6 came out. The 1st was since launch, I was unable to launch editor, as it would crashed and give me an error every single time, which since did get resolved but there's now another problem, as when I finally launched the PC Editor, none of my add-ons seem to be available to open under the content banner. I've got an image of what it looks like currently for me (and just so you know, I have a lot more content than what it shows here. If someone has worked out how to fix this by now, then I apologise for bringing this up and it would definitely help in this situation, but for now, this is just so annoying as I've managed to get launch the PC Editor, but I can't really do anything with it right now without the routes that I've got downloaded on my game.
If you haven't started the game since launching the editor, do that first (load at least until the main menu) so it can find the DLC correctly
Managed to fix this problem and it turned out to be pretty easy. On the bottom right hand corner of the content browser, click view options and make sure you have the 'Show Plugin Content' enabled. That way, you'll be able to see your DLC's in the PC editor. This is the image I got from trying to get help via support, but I feel it's worth sharing here, just in case anyone else is having the same problem that I had.