This was genuinely really fun. Great graphics and character, the levels are mostly quite simple but as you mentioned in your video they're only for testing so they could easily be made more complicated or used as early levels.
Bar the last one, that one was a nice head scratcher and I think if you tighten the space under the large block so that the magnet can't be forced in it would make for more of a challenge and force people to work out the puzzle based on purely game mechanics.
Finishing a level by grabbing a key only felt ok. What if you needed to move to a particular spot after getting the key? This opens up possibilities where you have to leave the magnet somewhere in order to reach the key (as in the last puzzle) but then once you have the key, there's a further challenge of how to get the magnet back in order to leave the level. Or might even allow for a Metroid Dread-esque level development where one puzzle could in fat be a way to open the door to other puzzles, perhaps by having multiple areas of a puzzle with their own magnets, some of which are only reachable by manouvering other magnets.
On the last level, I understand a lot of people jammed the magnet under the large block and I'll admit I did try that too but the game overall doesn't feel like the sort of game that wants you to do that sort of thing so I kept looking, I tried launching the magnet at the switch by perfectly timing a polarity reversal in order to use the the upward magnetic stream to give the magnet extra height an make it go farther which seemed like it could be a fun thing for other levels but again was far too difficult with this level so eventually I figured out the solution of having the door hold up the block until I was right next to it, giving me time to move past the second block before it dropped -which did fill me with a bit of panic the it might kill me for being to slow and reset the level.
Overall some really impressive work and a truely enjoyable game.