Hi dulcimer,
I gather when you are in Photos you see the desired pictures but within iMovie you get the message of "no media found".
I doubt you are missing something, but here are the two ways you can add Photos images to iMovie.
Add Photos images to an iMovie project - Apple Support
Use the Libraries browser in the iMovie sidebar
You can access your Photos library from within iMovie:
- In the left-hand sidebar of the iMovie window, select Photos Library.
- Click the pop-up menu at the top of the image browser to choose a content category—My Albums, Albums, Years, Collections, Moments, or Places.
- When you find the photo you’d like to use, drag it into the Timeline.
Drag and drop from the Desktop
You can drag photos from your Desktop and drop them into iMovie:
- Drag the photo you’d like to use from Photos to your Desktop.
- Drag the photo from the Desktop to the Timeline in your iMovie project.
If that isn't working see if this helps.
Designate a System Photo Library in Photos - Apple Support
Regards