The Movies folder is the default place where your iMovie Library would be stored. Try going to Go > Home > Movies and you should see your iMovie library there. If it's not there, then for some reason it is located in the Movies folder in the Library Containers Movies folder. The other library that you saw with only
Your iMovie library contains 124.66 GB of data. So pretty large. The other library that you saw with only 156 Kb in it is some extraneous blank library that got created when you either deleted preferences or updated.
As I mentioned in my previous post, deleting projects from the iMovie app will not remove significant space from your drive, unless you go one step further and delete the Event in the sidebar bearing the project's name, that contains all of the project media. You need to delete the event, not just the media in the event. That will remove the project and all the media that it contains from the iMovie library, and free up corresponding space. However, deleting media from the iMovie library will disable any projects that might be referring to that media. Also, unless you have the media stored somewhere else, such as a Finder folder, deleting it would cause you permanently to lose your media.
The solution to the space problem is to purchase an external drive, format it Mac OS Extended (Journaled) or APFS, and then Copy-Paste your library's icon in the Movies folder into the external drive. Before doing that, select the Library's name in the iMovie app media sidebar and do a File > Consolidate Library Meda. After copying the library to the external drive, verify that it is working properly. Then, if you want, delete the library from your original drive to free up space.
-- Rich