This goes to Geometry Dash without a doubt in my mind if you include user-created levels, and I do as long as they're officially rated with stars, especially if they're e.g. in a Gauntlet (which a number of Easy and Medium Demons are).
If you allow in star-rated levels outside of Gauntlets, then I think it's safe to say that Tidal Wave on its own crushes the difficulty of basically any video game ever made that's ever been completed by a human. GD is an interesting case where you can make it as easy or as difficult as you want because there's no true "ending" to the game (getting to the Demon Gauntlet is part of an actual storyline, but when you beat it, it goes nowhere, so that's weird).
if you include games with user-created levels there's quite a few games with levels that are practically impossible for a human, eg. trackmania and super mario world
As noted, "that's ever been completed by a human". Otherwise there's simply no ceiling; I can just create a game that requires you to perform 10 frame-perfect inputs every frame for five months straight and say "now I have the hardest game since it's technically possible to win; checkmate." With user-made levels, there's still a ceiling defined by a human actually completing it, and I don't think the human-beaten Mario Maker or Trackmania levels touch the extreme levels of difficulty at the highest skill levels of GD.
TL;DR: I think if we include user-made levels ever beaten unassisted by at least one human, Geometry Dash wins.
Do we have any evidence, though, that ChainChompBraden was exceptionally skilled and well-practiced going into this? Because to my understanding, the level ID for Trials of Death hasn't yet been made available, meaning Braden is the only one who was able to attempt this. Meanwhile, Tidal Wave was and has been available for literally anyone, and despite being the most prestigious level in a game where people pour tens of thousands of hours into beating near-impossible levels, it's only been beaten by two other people since it was verified last year, and these are the three best players in the game each with several tens of thousands of attempts on this level (they have god knows how many tens of thousands of hours of practice from other levels of similar but lesser difficulty).
Kaizo Mario can introduce some complexity that GD can't by having more than one type of input, but GD's hardest levels are so insanely precise (Mario Maker's 60 FPS or anything even near it would render top-level GD play essentially impossible) that even though these both push the limits of what humans can physically achieve, GD seems more difficult at its highest level of play.