First ALL Items has Model so DON'T use IHasModel.
Second use ModelLoader#setCustomModelMesher instead of Main#proxy#registerItemRender (Use in init stage)
ModelLoader.setCustomModelResourceLocation([YOUR_ITEM],0,new ModelResourceLocation([YOUR_ITEM].getRegistryName(),"inventory"));
And while registering items/blocks use List! don't use toArray() and you must enter your array size new Block[0] creates array with 0 size use new Block[ModBlocks.BLOCKS.size] !
@Draco18s anoher IHasModel user!