The plywood is this (Amazon).
My original idea was a jigsaw in the form of a maze of thin twisty paths that would cross itself frequently. But playing with that idea, it didn’t seem very workable; it would have to be huge because the ramps and bridges need to be somewhat gradual for the pieces to stay together. So I decided to try it with just one bridge and a very simple path. Then it needed some context (surrounding landscape) to be less boring.
I’m no artist, so I used DALL·E to generate the path a section at a time, then to generate variations on flower photos and to join the sections seamlessly, then to generate the figures (lizard, faery, cat, etc.) in context. The styles of the elements were initially inconsistent, but applying an artistic “cartoon” filter solved that.
Hasn’t been quite 4 years, but thanks for the welcome! 
I took a break from it after the Christmas project and tutorial. But now I’m working on some Civil War medallions, and some Civil War themed puzzles for a family reunion. (My father-in-law got really enthusiastic about an ancestor he found who fought in the Civil War.)
This Infinity puzzle was actually done last year, and I forgot to share it. I was still working on my technique, so there are a few flaws.