So, an update, if anyone’s interested: I’m now down to only four environmental puzzles yet to be found. One is on the town monolith, and appears to be somewhere in the vicinity of the starting area. One is on the shrine monolith, and there’s a very narrow slice of land where it could be, given the facing of the monolith, and given that too far in that direction would put it on the mountain monolith, instead. And two are on the mountain monolith, and appear to be somewhere in the vicinity of the polyomino marsh. There’s one there that I’ve suspected for a long time, but have never been able to get work, and it might just be useless residue from a different puzzle (i.e., the circle is real, and there are two paths from it, but maybe one of the paths just doesn’t lead to a valid endpoint at all). I have no idea what the other one would be.
Of the four panels I’m still missing, presumably three are the three above the timed-challenge vault, that change with the beat of the music (I got the challenge without those due to a bug). Which probably leaves one loose triangle-puzzle somewhere. I did stumble upon a method for finding where unsolved loose triangle-puzzles are, but it’s still tedious to find it and put it in context.
I think I’ll consider myself done once I get all the environmentals, and probably not worry about that last panel (nor about the many, many audios I’ve missed).