It's been a minute, but I used that Norbyte lslib tool to extract them from here
.wine-dos2/drive_c/GOG Games/Divinity - Original Sin 2/Data/Textures.pak
All of the menu paintings were by themselves in one dir (can't remember the name), and the individual textures had names like this
MENU_NewGame_Painting_A_Active_BM.dds
MENU_NewGame_Painting_A_Inactive_BM.dds
The inactive ones (paintings w/ cool tones) were ~22M 4K textures, the active ones (warm tones) were ~3M 2K textures.
