Q: Full size photo appears black in Motion

Launch Motion

Create a new project

First thing in the new project do a Shift-Z to scale the canvas to the window pane, so you see the whole thing.

If you still aren't seeing it, I'd ask this:

What is your Motion project's frame size?

What is the photo's frame size?

What is above the photo in the Layer's pane?

Screen shots help, too.

Looks odd.  When you play back the timeline, does that first photo every actually show up?

Have you verified Opacity and such in the Inspector for that first photo?

If you drag the photo in the timeline to the left a little, does it show up?

A couple of things...

First  as an FYI, in your second image, second example the reason you don't see the name is that in pictures 1 and 3 you have change the image to enable drop zones. That's why the name shows up in the canvas, also notice the icon difference in the layer list.  At this point, you don't need to deal with these options and you will want to leave it un-checked.  The main options you will probably need to be looking at are the Properties  tab, or maybe even the media (select the image and then type shift-f).

I would shift tact a little bit and ask about the source of the image.  I see it's a jpeg, but what type of camera is it from?  You said that older images work, do any image from this camera work?  Also what about your computer, what more can you tell about your setup, it's always  good to post a few more specifics with Motion and Final Cut, this often includes the OS version, RAM, app version number, graphics card. These details can all be important. Is all of your software up -to-date? Finally, can you post the original image someplace,it might be good if someone could try with the same media?

If your image has compatibility issues, try opening the image up in Preview, then File > Export a new copy of it using Format JPEG or PNG (and vary its name so you don't overwrite the original). You can replace the image in Motion with the new image by finding it in the File Browser tab and dragging and dropping the new image on top of the Layers List reference of the original image (you should see a right-hooked arrow). That will keep whatever else you have in the project in consistent with what you've already done (or tried to do) with the original image. You don't have to worry if you change image format from jpg to png either. Motion will quite happily replace the original with whatever you want (even video—there is an exception, but it won't apply here [has to do with replacing video only with video+audio or vice versa].)  PS - if your original image is extremely large (like 18+MPixels or so) try scaling it down about 25% before importing into Motion... This might be necessary if your video card has 256MB vRAM or less. Motion has a peculiar habit and long history of ignoring elements it can't handle (due to hardware limitations) while continuing to run without complaining.

Glad you worked out a solution.  FWIW, instead of doing screen shots, you could also try using the Export option in Photos (shift-command-E).  I'm guessing this generates a new file and might save you a few steps.  I'm still really curious what your camera source is?  It seems like that might be part of the issue.

although you solved your issues, have you tried this advice?

Set graphics performance on MacBook Pro - Apple Support

... just to feed my curiosity

I vaguely remember something with UHD and openGL and drivers and stuff (not my main habitat, you notice) ....