Hi,
iMovie 9 is not completely functional on operating systems from El Capitan and later, including High Sierra. Faded videos have been one of the complaints. Black screens with photo still images is another. So that could be the problem. If you share out the video it might not be faded in the final product. Try it with a test project. Otherwise, there really is no solution other than to upgrade to iMovie 10. As a workaround you might be able to apply whatever clip adjustment features that iMovie 9 has to eliminate the faded look. Anyother thing you could try is to open the video clip in QuickTimePlayer and export it out at a lower resolution. Sometimes that cures issues.
To upgrade to current iMovie 10 you would need to be running at least Mojave 10.14.6 or Catalina operating systems. If you are able, you might consider upgrading to one of those. Here's a link that describes how to upgrade to Mojave:
https://support.apple.com/en-us/HT210190
However, if you have, or ever had, iMovie 10 on your computer you should be able to download the highest iMovie 10 version that your present operating system will run. I realize that you've said that you cannot find iMovie 10 in your app store purchases folder. To confirm that you have followed the correct redownload procedure do the following: Drag your iMovie app from the Applications folder into the trash (you can skip that part if you have already deleted iMovie 10 in the past) , but do not empty the trash. Then sign in to the app store and open your purchases folder by clicking on your name at the bottom of the app store side bar. You will see your purchases displayed, hopefully including iMovie. Redownload/update iMovie from there. You should get iMovie 10.1.8 I believe. If not successful, drag your present iMovie app out of the trash (if you put it there) and return it to the Applications folder.
-- Rich
