/ ! \ Fixed in the latest build, go grab it instead.
I haven't dived in the new update but when i checked the fanart gallery, some pictures wouldn't load and gave me the following message "image fanart <name> not found.".
So i looked a bit in the code and in the file game/imageDefines.rpy added theses lines (462~465) :
image fanart IsaacDrizzle = im.Scale("bg/fanart/IsaacDrizzle.webp", 1920, 1080)
image fanart IsaacNexiNexal = im.Scale("bg/fanart/IsaacNexiNexal.webp", 1920, 1080)
image fanart IsaacWen = im.Scale("bg/fanart/IsaacWen.webp", 1920, 1080)
image fanart IsaacTempest = im.Scale("bg/fanart/IsaacTempest.webp", 1920, 1080)
image fanart IsaacSabre = im.Scale("bg/fanart/IsaacSabre.webp", 1920, 1080)
Don't know if i messed up somewhere or if these lines are really missing but in case someone have the same issue, there you have the fix.