I have a Andoku, a sodoku game that was open source and had the perfect setup options for selecting and placing numbers.
It got sold, and new devs immediately added ads and broke everything. I think it's some sodoku 3 with subscription options now. Been running it since probably 2013ish.
My SO and I play as a team across dinning tables in restraunts while we wait for waiters or food or whatever.
Upvote for xnview, have you tried the MP version, or whatever it is. I think I run that now, but I have both installed still.
I actually just removed an old portable version that was just living rent free in my portable apps folder for years.