Yeah, I knew some place will be hard to figure out, the lack of playtests shows:/ You should grab a ring in a room after the first powerup, before the trapped miner moles. If you get there, you have to open the gates again and You should see this, like in the picture. But its still easy to miss I agree...
The vertically is there because I wanted to do it, but its hard to be done when You have a platforming hero jumping high... So it became an issue I haven't addressed yeah. I don't know if moving camera away even more would work, because then it would get weird in tight corridors. Hm. But in the end You aren't really required to do many steep jumps - outside of maybe mushrooms at the beginning and once in the end. But I know that people will try when they're lost.
And yeah, I messed up about shadows:D I really thought that this game would be a bit more fleshed out, more enemies, more QoL features, but it turned out to be more difficult than I expected...