Hello fellow dev, can see the spark of something promising. Here is my feedback, hope you take it in the spirit it's intended.
Entering and Re-entering Levels:
-Currently the player gets trapped should they re-enter a level after completion. While they can use the menu to exit, something like having a 'ghost key' as the end condition should be present so players may re-attempt should they desire. Additionally, It is my belief that players should never have to touch the in-game menu for anything unless they desire, so having an in-game way to exit to the HUB would be nice - such as the door lol. Intuitively I wanted to press up at a door to enter/exit, and use the pipe to unlock the gate, but the pipe was essentially the door and the door was purely visual.
HUB and HUB Feel:
-The game is a puzzle platformer, but the HUB is a flat hallway. All aspects of the game should provide some sort of gameplay, so the HUB is a great place for simple platforming. Players find enjoyment in just hoping around, so this would be a great place for players to cool off between puzzles with a playground of sorts. Expanding past this idea, the HUB additionally could be a puzzle itself, where players need to figure out how to unlock the gates to the levels. The pipe's could be the locks, and the player needs to figure out how to open the gates to attempt the levels in whichever order they choose.
-Level 7 is dramatically harder than the rest. If you are going to put in unrequired extra hard levels, I'd suggest marking it someway in the HUB (such as making the gate red), so players understand they are taking on a bigger challenge. Doing this helps players know that should they fail, the level was designed harder, rather than their intelligence wasn't on par.
-The finish line gate doesn't really make sense as designed. Visually, you use old timey keys in your tech facility, to open the final gate, but the individual keys are also needed to open each level? Maybe gate each level with something else (or not at all), and change the final gate to open with 'completion' powerlines streaming from the individual levels. Simply changing the key to a powered generator, and changing the Mario sewer pipes to a mail vacuum tube might help with the visual language that is trying to be communicated. Lastly on the topic of HUB art, it has parallax scrolling, so it looks like the gates are floating in place when you walk past them.
Gameplay and Gameplay Feel:
-Getting the clear condition felt abrupt in some levels, as it didn't feel like that should be just the end. I felt since it was a puzzle platformer, that I would have to get the clear condition, then platform back out of the level past the mess I made - proving I fully understood the central gimmick of the puzzle. This would allow more moments for the player to mess up in the homestretch creating those 'lmao I'm so dumb' moments that were unfortunately missing. Funny mistakes are almost required in a game that has a cute art style like this, as well as other ways to inject some levity.
-It wasn't immediately apparent that jump height differed whether or not you were holding the magnet. This made the character feel buggy until I realize it, and even still felt off knowing that detail. I can imagine some players not figuring out the variance in jump height thing, and putting the game down out of sheer bad control feel.
-One level had a metal box with a magnetism symbol on it. As most people associate metal and magnets already in their head, this redundancy actually made figuring out how the metal box worked more confusing, since it could be mistaken for a unique object to your game world with the additions.
-There were a few areas I got stuck in and couldn't platform out of, forcing me to restart the level. Restarts can feel like failures to players, so it's best your levels don't require them in instances. More testing for environment soft locks.
-Lastly, played on an Xbox controller, and the level restart was set to 'LB', but the symbol around 'LB' was round, not matching the shape of the controllers button. While obviously the most minor thing to point out, it's important to point out every minor thing, as game feel can be eroded by stacks of minor things like these that are written off as unimportant. Many AAA games leave very minor things in their games, and I believe this mentality has lead many devs to cut corners in quality in other aspects of their games. Your the teacher youtube guy, so want to help you continue to bonk out bad practices in the industry.
Overall, good work. Obviously there is still a long way to go before this is a complete game. For this to become something I'd pay money for, I'd personally want to see more personality, character, and humour baked into it. Currently, feels on the reserved end, and I'd encourage leaning into the weird once you're happy with the overall mechanics and whatever else you need to add for your videos. I never played the original, but stand alone it's got a solid framework form something good.