Finally I know how these puzzles are called, I played something similar before :)
The difficulty is a bit high, not sure if your code would allow easily creating smaller grids, but ramping up the size would give a nice difficulty curve. (Later I found "easier mode" in settings, but I'm not sure what it does)
UX is very nice. Visuals are minimalistic, but cohesive and pleasant and sfx improves the experience a lot.