Solved, and it was fun! But...some of the colored lines were hard to see. Particularly the light yellow ones. I had one "alternate" solution that it was marking incorrect for reasons it took me over a minute to spot...and it was just a super light yellow line I missed without really scrunching up to my screen.

Improving the color choice might help, but slightly thicker lines I think would also be of significant help.

Also, it's common for sudoku solvers to allow you to press Shift+number to do a one-off toggle for the "note" checkmark.