I am a beta tester and think this game could go very far with a cooler appearance and effective marketing. You should definitely post a video and screenshots on here as those would attract way more people.
What a fascinating concept; I've never seen Sudoku converted into a roguelite before, and I also appreciate the keyboard support with numbers. I'd request further keyboard support with arrow keys for box navigation and Enter or the space bar to set numbers.
I recommend using a fancier serif font, and allowing the back button to back out of the descriptions of new abilities at the end of levels (instead of having to tap the "X" icon).
There are some other, very minor issues like the description to the pentagram-shaped ability: "At the start of the Level" (instead of lowercase "level"). Additionally, you may want to find a way to reword, "reveal one of the most placed uncompleted digits" (the Z ability's description), because that's a bit odd to read; what about, "reveal another one of your most filled digits," instead?
You will also want to add sound effects to every single event; for example, there is a sound that plays when you back out of reading an ability's description, but there is no sound when you first pick the skill to learn more about it. There should also be a sound when you complete a level, when temporary shields get set or fall off, etc.
I wonder if there should be a money system to buy (and sell?!) abilities, because some of these abilities are really imbalanced versus others!
Additionally, balance-wise, I kind of wonder if placing a duplicate number in a box should be less punishing with only half-health deduction instead. Just my thoughts given how limited the health is...
Lastly, be able to disable haptic feedback in the options for vibration haters.
Really great work with the creativity and implementation thus far, and I mean that! I'm glad I randomly came across your game while browsing. You may wanna delete the old versions or put them at the bottom as common practice across itch.io seems to be to put the latest version at the top of the downloads list; I was a bit confused by that at first.
Update: While I love how there's an endless mode, it erroneously gave me the win-1-run achievement even when I died on level 9/9. I also note that the pink linker ability keeps playing its two-ping new-link sound even when it can't establish a new link (due to there only being one remaining tile on the board to fill).
Then I came across a bizarre bug which made me wonder if you have a logging system for bug-tracking: I happened to beat level 9/8 by dying on my very last move, which triggered the pink linker and either an odd or even chain filler (I had both abilities by that time). It said I died, then it showed the victory screen, and then it showed the details for level 10/8 to proceed, and then it game over'd me. I feel like if you happen to be able to beat a level through your abilities with no health left, the game should honor that achievement and give you half a heart to keep going, haha.
I do honestly wonder if this game could go viral and wildly popular with a rebranding to "Roguedoku" or something, with multiple game modes (there are numerous variants of Sudoku out there if you study Simon Tatham's "Solo," like mathdoku or a version with slithering box lines, a letter mode with 9 random alphabetical letters or even from foreign languages for students' character-training recognition instead of 1-9 or something, etc.); personal if not also online high scores; a casual/untimed mode with no time-related abilities and its own, separate high-score board;' a dark theme; etc. I'm not sure of what marketing you've tried for this game, but I'm fairly sure that no one has even remotely executed anything close to this incredibly original take. All it'd need is some tinder to catch the whole Internet ablaze for more. Online high scores are a big deal to people.
I would say that one of the biggest things holding it back is its presentation. Interactiveness (like every single possible action and button having a sound effect, like in Zelda) and presentation matter a tremendous deal in hooking people. I suggest you check out Glass Masquerade gameplay videos to see what I mean; even that game's menus are gorgeous!
Update: Okay, I do have to say that I find it annoying that the timer keeps counting down even before the numbers have been added to the board. This is especially frustrating in the endless mode marathon in which the timer doesn't reset between completed boards.