Mods

What vemerion said will work because deferred registers need to be registered on the Mod bus...while with this code: IEventBus eventBus = MinecraftForge.EVENT_BUS; EntityInit.ENTITY_TYPES.register(eventBus); you are registering your deferred register to the Forge event bus, which is where in-game events are posted. Registry events (for items, blocks, entities etc....) happen during the loading of the game and are posted on the mod bus (which is different from the forge bus), which can be retrieved with: FMLJavaModLoadingContext.get().getModEventBus()  

INameable#getDisplayName that's applied to every single entity.

1.15 and 1.16 are different versions of the game and aren't compatible internally, by contrast 1.16.1 vs 1.16.2 the update is (usually) a bugfix update so there's no point staying on the version with the unfixed bug

It's LTS, so forge still supports it. Also, this problem really isn't forge's issue. It's usually gradle screwing up somehow that makes you want to pull your hair out.

Provided you already know Java language (which is a must if you want to create mods)...there are many tutorials online, some are good and some not very much..it depends also on how you prefer to learn things. You could find modding videos to be more appealing to you than to read giant walls of code..but i should warn you that youtube tutorials won't get you very far into minecraft modding, and also do not teach "good code practices" very well. I suggest you just watch the first tutorials (items, blocks..) to get a very general idea about the modding workflow, and then to move to better tutorials. There are many example mods around, just waiting to be read..you can for example take a look at Cadiboo tutorials or GreyGhost's, both are very good. When you get a better understanding of what you are doing you can start looking directly into other people mod's code, since lot of them are open source. There you can see how they handled various situations (which you may find yourself into someday). Finally you can look into vanilla minecraft code. For example you may want to create a mod that implements a certain thing..and if you don't know how to achieve what you want, the first thing you should think is: "has vanilla minecraft already something that is even remotely similar to what i want to do?". If the answer is Yes then just look how they did it and try to understand it...then you can probably use the newly acquired knowledge to solve your own problem. If vanilla minecraft code cannot help you then you can try to search for mods that add something similar to what you want to do (read their code, understand it, repeat the process 😉). As a last resort you can always ask for support on this forum...That's basically how you learn this kind of things...once you get the basics, try to do something by yourself, read code that was already written by others and try to get to the solution only with your mind  before asking others for a solution. Hope what i said will give you a little bit of a direction to follow and i will end this post saying what i said in the beginning, because its a crucial point that a lot of people trying to make mods are ignoring: Java knowledge is your best friend here