Something very strange is going on about your gradle cache with files randomly disappearing. Delete it again (as instructed above) and try again. I would also recommend you check that your drive is still working properly.
Don't do this: https://github.com/ArianKG/KGForge/blob/main/src/main/java/com/kg/kgforge/init/Init.java#L7. Do not store the event bus in a static field.
Do not put a DeferredRegister and its entries in separate classes. You will cause issues.
Do not create registry entries (PaintingType and EntityType in your case) in a static initializer. It must be done in a registry event, DeferredRegister is recommended.
You must register a renderer for your entities using RenderingRegistry.registerEntityRenderingHandler.