iMovie missing source file

Utterly disappointed with my first Mac purchase ever. I have a 15" MBP and it's been nothing but headaches and stuck keys.

I connected my Lumix G7 camera to the machine, imported the videos as I do into Photos.

Opened iMovie, started a new project, imported the 3 clips I wanted. Everything looked fine. Couldn't export the file or save it so I simply clicked back to Media from the Project tab within iMovie as I'm new to the software. Anyway comeback into the Project and the yellow ! box is surrounding each of the 3 clips saying source file missing.

Well the source files are sitting on my camera, AND are in my Photos Video tab. Can't access either via iMovie. Also when I try to important media for iMovie directly, can't even find my Photos library.

Unreal how a company so rich can make such god-awful hardware and software and people keep coming crawling back. I've been duped by the Mac craze. Thankfully it was only once, and will only ever be once.