Unless you hate the art style, the Atelier Games (especially the newer ones, like the “Ryza”-Trilogy or “Sophie 2” that got rid of the time limit) are definitely worth a look!
And if you enjoyed Stardew Valley, then Rune Factory might also be worth a look: the newest entry (5) is the first mainline 3d-title, which was a divise change (especially due to not amazing performance on the Switch), though I enjoyed it; but the “Special”-version of part 4 is also worth a look (if you can stomach the 3DS-style visuals)
This is very cool! Coming from a beginner, it might make the first few games easier if you added an extra setting that would start the puzzle with one or two numbers already filled in (like a typical sudoku), as that gives a natural starting point. Obviously, it may not be needed if you mainly develop this for yourself :)
I believe in the Puzzle I attempted, the solution was not unique: at the end, two numbers could be placed interchangeably (in my case, I could switch around all "1"s and "4"s and end up with just as valid a solution - that is, of course, unless I missed something :)
Very cool little puzzle, thank you for sharing!