I think the answer is shown in your screenshot: all those extra features are already installed! Hence, there is nothing further to be added to what you already have.
Whether true or not, the installer clearly believes they are installed and so you cannot select them! My understanding is that the installer checks your computer’s registry so it is showing them as installed. If they are not, I think that this would suggest that, somehow, they have been deleted but not uninstalled. Uninstalling them would have removed the associated registry entries. So, have you ever had any of these “extras” installed for any earlier version of MEP?
Yes, I did have the entire media pool (transitions, menu templates, subtitle templates) in all of my previous versions of MEP. For some reason, they are all gone now after installing MEP Premium 2022. I even tried uninstalling and reinstalling the program, but to no avail. Has anyone else run into this issue?
I even tried uninstalling and reinstalling the program, but to no avail.
Nooo. Don't do that. You can easily make things worse. Everything should have been there. Now that you have uninstalled, no one can say except you.
The additional content is now normally in a folder that is used by each version such that you don't have to install certain additional content if it is already present. That is why it shows that the content (probably not all of it) is already installed.
The image that you showed at the beginning, is it from MEP2021 or MEP2022?
In MEP2022, I think that about the only thing that has changed is Travel Maps, which should now be at version 1.2 something.
So that you know, the additional content gets installed under:
C:\Users\Public\Documents\MAGIX\Common\Videocontent\Movie Edit Pro Plus
or
C:\Users\\Public\Documents\MAGIX\CommonVideocontent\Movie Edit Pro Premium
Note that there is no version indicated because each new version just updates and/or modifies or adds to what is already there, saving you having duplicate files and having to install everything each time.
If you have nothing there, the I expect that you will have to download and install everything.