Migrate imovie projects

There may be other ways to do this, but below is one way.

Edit/Copy, Edit/Paste your iMovie library to an external drive that is formatted Mac OS Extended (Journaled) or APFS. Then plug the external drive into your new Mac. Then you can copy/paste the library from the external drive to your new Mac's internal drive, or you can leave it on the external drive from where your new Mac's iMovie app will open and access it.

Before copy/pasting your iMovie library from the internal drive of your old Mac to the external drive, select the library's name in the side bar of your old Mac's iMovie app's media pane, and do an Edit/Consolidate library media. That will insure that all of the media in the library is carried over to the external drive.

Note that if your new Mac is running a newer version of iMovie than your old Mac, the first time that you open the library from the new Mac the library will update such that the older iMovie app on your old Mac won't be able to open it. So, I would leave the original duplicate copy of your iMovie library on the old Mac in case you want to access your previous projects from the old Mac.

Read this Apple support link for more details on how to transfer or copy an iMovie library to an external drive:

Move your iMovie for Mac library - Apple Support.

The above link suggests dragging the library, but I like the copy/paste method better because it is safer.

-- Rich