All of these methods are pointless, just call setRegistryName instead of calling a wrapper function that calls one line of code.
https://github.com/eddie1101/PortalTest/blob/c26623c062770115212536c540219f7abda1091f/src/main/java/erg/voidcraft/common/util/Util.java#L12
All of the declared types of these can just be Block
https://github.com/eddie1101/PortalTest/blob/c26623c062770115212536c540219f7abda1091f/src/main/java/erg/voidcraft/common/block/VoidcraftBlocks.java#L10-L14
Also, you haven't @ObjectHolder'd them, so you're not even using the thing you said you are in your thread title.
You aren't registering any blocks or items, because you haven't registered your classes with the event bus:
https://github.com/eddie1101/PortalTest/blob/c26623c062770115212536c540219f7abda1091f/src/main/java/erg/voidcraft/common/Voidcraft.java#L40
(You also aren't using the @EventBusSubscriber annotation)
Or the @SubscribeEvent annotation:
https://github.com/eddie1101/PortalTest/blob/master/src/main/java/erg/voidcraft/common/block/VoidcraftBlocks.java#L16