A brief explanation of Nonograms/Picross:
Nonograms are a form of picture puzzle where you build things (typically a whole picture) out from a pixel grid from as few as 5x5 to absurdly large 20x20 puzzles. A number or several numbers will be placed along the border of rows & columns indicating how many of the squares need to be filled in.

Picross is the Trademark name of the same concept, as produced by or under license of the Jupiter Corporation of Japan.

Murder By Numbers is an example of a nonogram game, except it has the same problem that many serviceable puzzle games have: Far too much anime.

As far as I can tell, that's literally the only Nonogram game on GOG at this time. But I was wondering if any of the forumites have suggestions for others. (DRM free preferable, open source even better.)

if you go to sites focusing on casual games, for example Big Fish, you will find tons of them, same on Stem.
here is s bundle with 28 nonogram games - https://store.steampowered.com/bundle/8770/Picross_Bundle/

If you search for Simon Tatham's Portable Puzzle Collection, the one called Pattern is a game that randomly generates nonograms of various sizes for you to solve.

I am aware of the Simon Tatham Puzzle Collection, it's wonderful.

Voxelgram is a good take on the Picross 3D formula. Oh neat. Didn't know about this one.

I like the concept, but it just feels too big brain to me.

The Chris Boyle port to Android is good stuff. Open source