iMovie -- external volumes

The iMovie app itself hardly takes up any room. The movies and data are stored in the iMovie Library that you will find in the Movies folder on your Mac. You can copy-drag or Copy/Paste the iMovie library to an external drive that is formatted Mac OS Extended (Journaled) or APFS. Copy it over first and, if everything is working properly with the library on the external drive, you can delete the original library. Be aware that if you need to reformat your external drive the reformatting process will erase all data on the drive. So back up elsewhere any data that you want to keep.

-- Rich

iMovie will open in the last library in which it was opened. To open in another library, click on File/Open Library/Other and navigate to the location of the library on the external drive that you want to open. Once you open in that library iMovie will continue to do so the next time you open iMovie. Or, you can go to the external drive and click on the iMovie library's icon, and it will open in iMovie.

-- Rich

Another way to open in a library of your choice is to hold down the Option key as you open iMovie. A selection box will appear with library choices.

-- Rich

You are welcome! :)

-- Rich