Found this project called Wallhalle.

The guy behind it got a 4K and then a 6K monitor and he started curating his favorite paintings and digging into artists he didn't know, just added new works, cleaned up edges, and added support for sliced paintings so non-widescreen ones work too.

Name's a play on Wallpaper + Kunsthalle (German for "art hall") + Walhalla/Valhalla. No profit, just sharing classical art in resolutions that are hard to find.