Well, a full uninstall seemed to do the trick. Now, I can finally switch between versions. But now there's a new problem.
It used to be that, if I saved a project in one version and then switched to an earlier version, I couldn't pull up the project because it relied on a later version of the software. However, if I (A) saved in one version, (B) switched to a later version and made some edits, and (C) switched BACK to the version it was originally saved in, I would be able to continue. The only thing I couldn't do is switch to a version that was earlier than the project was originally saved in.
So I've made a habit of starting my projects in the earliest version possible, so as to maximize the number of versions the project is compatible with.
However, since I did the full uninstall, I've worked on a project that was initially saved in version 7.00. I then made some edits in version 7.05, since that was the only version compatible with my license that allows me to use "crop and zoom" when I export so I can get a vertical video for Youtube shorts. I then reverted back to 7.00 to continue my work, but it said that my project wasn't compatible with this version, even though it's always been compatible before. I was forced to finish the project on god-awful v7.05.
Aside from that one feature when I export, I detest v7.05. It introduced a lot of features that are more of a hinderance than a help, including but not limited to ...
adding "title text" when I pull up a text box (forcing me to delete the box to add my own text, creating a pointless extra step that wouldn't exist if the box was just blank)
Whenever I take a snapshot, any transparent sections of the image would be filled with black, instead of transparency.
It's generally just all-around less stable and tends to clog up my CPU even when it's sitting idle.
For all of these reasons and more, I generally prefer to only use v7.05 for the "crop and zoom" export feature, and nothing else.
I can't afford to upgrade to a new license (and even if I could, I've noticed that a lot of the latest versions still have that aforementioned "title text" garbage, so I probably wouldn't want to), but up until now, I've never had a need to. Simply switching back and forth between v7.00, v7.03, and occasionally v7.05 in order to make use of each versions' features has served me well.
But if I can't revert to an earlier version within the same project like I used to, that's a problem.
But it shouldn't be a problem. It's never been a problem before.
So do you know how I can fix THIS?!