Movie 10.4
How to import pictures from Photos into IMovie10.4
iMac (2017 – 2020)
Question marked as
The recommended way is to click on the Photos item in the iMovie sidebar. That will display in the media browser your Photos library photos. From there you can drag them into the time line of an iMovie project. For this to work you must have your Photos library designated as the system photo library in the Photos app general preferences.
Another way is to File/Export from the Photos app to your desktop, and from there drag into iMovie.
I believe also that you can directly drag from the Photos app into iMovie, though not 100% certain of that.
— Rich