It took over two years before 3rd-party software could break Nintendo's DRM and give players the privilege of seeing how someone else's level works:
https://github.com/JiXiaomai/SMM2LevelViewer
and even that effort only evaded a ban for a month or two:
But you're right that it's frustrating if you're starting out. Many Troll makers provide a "behind the scenes" version where you can inspect how the contraptions work e.g. adding a vine you can climb to see mechanisms "above" the level, or making something transparent or whatever.
I think trolls are the category where off-screen mechanisms are most important. In a puzzle level they're mostly an unnecessary confusion (where did that key come from? Well, off screen a Thwomp hit an ON/OFF switch and...) and in Kaizo who has time to look at everything on the screen, let alone think about things that aren't on the screen.
Of course once you're actually "Into" it there are private discords and so on for discussing stuff where people upload video, provide codes for their "Uno mas" demos (ie very short courses that show off a single new idea) and explain insights into the underlying mechanisms. I never got that deeply into MM2 but it's clear that people writing trolls for Carl or Geek are co-operating.
†A "softlock" is when it's possible to get into a situation where the player can't win but they also can't die and start over, so they must either restart the game or wait for some in-game timer to count down to zero. In normal course design you should prevent this, if necessary with an "anti-softlock" where Mario assuredly dies once frustrated in this way, e.g. you miss an important jump, and Mario just falls to his death, rather than being stuck in a deep pit from which he cannot escape. But in troll design you make dying in this circumstance possible but extremely difficult, so that the player's skill in tested not only in winning, but also just in dying. This art is called an anti-softlock or most often "anti" for short and is a crucial part of "troll Mario".
That's not even on a general purpose computer, a Switch is something you might have purchased or been gifted solely to play video games and now you're a level designer, able to show off your aesthetics, pacing, mechanics and so on.
(Java) Minecraft is way beyond that because it's not even just about level design, it goes way beyond even a Doom TC. People change the physics rules, how graphics are rendered, not to mention radically changing the gameplay. I basically only play the ascend-to-godhood type packs, and even among those there's so much variety between something tightly themed like Compact Claustrophobia or Star Factory, and big sprawling do-what-you like packs such as Stoneblock, or Project Ozone. But now you're a video game programmer (albeit in Java) not even just a level designer.