iMovie 6 projects cannot be updated to iMovie 10. However, iMovie 7, 8, and 9 projects can be updated to iMovie 10. I'm not running Catalina or Big Sur so not entirely sure that 32 bit iMovie apps can be updated in iMovie 10 if you are running Catalina or Big Sur that do not support 32 bit apps. But it doesn't hurt to try.
The first thing to do is to make sure that your iMovie 7 and 9 Projects and Events folders are located where iMovie 10 can find them. They should be in the Movies folder on your internal drive, or at the root level (i.e, not in any folder) of an external drive.
If all O.K. there, then open iMovie 10 and do a File/Update Projects and Events. If you get a message saying that there are no projects and events to update, and you know it isn't true, then go to your Movies folder and open the iMovie Projects folder. If you see in there a marker that says "UpdatedToiMovie10", then delete that marker. Do the same with the iMovie Events folder. Then try again to do a File/Update Projects and Events from within iMovie 10. If still no luck you may need to copy out the media in the iMovie Events folder and import them into a new iMovie 10 project where you can start over with a re-edit. In other words, recreate the project.
-- Rich
-- Rich
