BlockInitializer.java:37: error: cannot find symbol
void registerBlock(CreativeTabs targetTab, Block block, String blockName) {

Solution is to removed addition to a creative tab (and hope that the block magically gets registered to the tab/item group).

Please notice that it can be observed in some 1.14 mod that blocks are registered with an item group then same way items are added to and 1.14 item group.
Link: https://github.com/zwang3583/Ores-o-Plenty/blob/master/src/main/java/com/huihuiz/oresoplenty/OresOPlenty.java:

@Mod.EventBusSubscriber(bus=Mod.EventBusSubscriber.Bus.MOD)
    public static class RegistryEvents {
        @SubscribeEvent
        public static void onItemRegistry(final RegistryEvent.Register<Item> event) {
            Item.Properties properties = new Item.Properties().group(setup.itemGroup);
            event.getRegistry().register(new BlockItem(ModBlocks.RUBYORE, properties).setRegistryName("oresoplenty","rubyore"));

Other examples:

• https://github.com/Aeronica/fourteen/blob/master/src/main/java/net/aeronica/mods/fourteen/Fourteen.java
• https://github.com/MobSlicer-Owner/DungeonCraft/blob/master/src/main/java/ca/randomcode/minecraft/DungeonCraft/DungeonCraft.java

Closed with commit f5cdf57.