According to your screen shots you are using iMovie 8, that is a 32bit program and not compatible with Catalina. Further,
iMovie 8 can no longer be updated at all under any circumstances because it is an obsolete program no longer sold by Apple. Thus there is no path to an update of iMovie 8.
Try signing in to the online app store and downloading current iMovie 10.1.13. First, see if in your Applications folder there is an iMovie 10 version. If so, drag it to the trash, but don't empty the trash. Then open your app store account and check your purchases list. If you ever had iMovie 10 running on your computer there may be updates available. If not, type in "iMovie 10 app" in the app store search box and see if you can update or download iMovie 10 from there. If for some reason you cannot get a download or update, then move your present iMovie 10 app (if you have one) out of the trash and back into your Applications folder.
Once you download iMovie 10 you can, from within iMovie 10, do a File/Update Projects and Events to update your iMovie 8 projects into iMovie 10. I'm not sure whether that will still work since iMovie 8 is not compatible with Catalina, but it is worth a try.
-- Rich