The latest update stated that the save error was not fixed. But personally, the error disappeared for me. I can't say what this might be connected with. I only replaced the folders and files specified in the last post.
I checked again (2). In fact, the file can only be saved in the mod folder. If you try to save in the game folder after moving from the mod folder, an error will occur. If you try to save again, the error will disappear, but the level will be saved in the mod folder. Wtf?
