iMovie Library Access

Instead of "Custom Access" change your permissions to "Read/Write". Same with the new library that you create per my previous post.

Also, take a look at this thread, particularly the solution at the end, and see if anything in there helps you.

https://discussions.apple.com/thread/250842188

-- Rich

Shut down your computer and reboot. See if that solves it. If not, do the following:

Control click on the library's icon and Get Info. At the bottom of the Get Info box make sure that you have read and write permission.

Also, control click on the external drive's icon and Get Info. At the bottom of the Get Info box there should be a little box that says "Ignore ownership on this volume". If the box is not checked, then check it. You will first need to click on the little lock symbol and sign in with an administer name and password.

After doing the above, see if you can open your iMovie library.

-- Rich

Try creating a new empty library on your external drive. Then copy into it one of the projects from your old library and see if the new library will open. To copy the project, open both libraies and go to the projects browser view on your old library (where your projects are displayed as icons) and move your cursor over the title of one of the projects. Click on the little circle with dots in it that appears to the right of the title. A drop down menu will appear with the option to copy the project to the library that you choose. Chose the new library.

-- Rich

Is your library located on an external drive?

-- Rich