Honestly, the portal thing is a pretty small one time thing but thought it was worth mentioning.
The visual noise thing is tough but I feel like having a dark or light outline on the foregrounded objects or adding a layer on top of the background that made it darker would've done a ton with very little effort. Just some ideas.
And in case you haven't seen it, Game Maker's Toolkit has a really helpful interactive video essay about platformers and making them feel good that I found very helpful. I run through this almost every time I make a game lol