Personally I think that Elixir is easiest language (especially when learning as first language as you do not have any OOP language in mind).

The most important part for developer is how nice code (to read quickly) you are able to write (Elixir have awesome builtin support for lots of things like documentation) and how much code you need to write in order to achieve something.

(…) The new code is about one-tenth of the size of the old code. (…)

Source: An introduction to the Elixir programming language | Kyan

Other threads which may help you:

1. What is your number one tip for anyone new to Elixir?
2. Your Elixir Tips Thread
3. Elixir’s biggest gotchas?

Elixir would be a fine choice for learning back-end development, though I’d recommend learning Elixir by itself first

If you already know Javascript then Javascript would also be a good option for learning back-end development.

The Elixir ecosystem is great for backend programming. A great introduction would be Dave Thomas’ course, Elixir for Programmers. There you will learn how to create a backend game engine and a frontend game client that will give you a solid foundation for understanding Elixir. Good luck! And Welcome!

That original link is dead. I think it was this article on code academy. Back-End Web Architecture

Dr. Stephen Strange: They really should put the warnings before the spell.

Ryan Dahl, Creator of Node.js:

And honestly, that’s the reason why I left Node. It was the realization that: oh, actually, this is not the best server-side system ever.

Node.js as a Backend: Best Use Cases, Tools & Limitations

Advice for choosing between elixir and nodejs

If you just want to get your feet wet start with Getting Started and continue with Mix and OTP to see if you’ll have any problems.

• There is nothing special about languages that are being used on the “back end”. It just happens that originally JavaScript was designed with the runtime constraints of the browser in mind - so at the time there was no need for language features that are considered essential for large scale application development - and the Node.js community has had to backfill the holes ever since (e.g. adopt a module system before the official language specification did).
• Being comfortable using the command line would be helpful. By extension in my personal opinion I think it would be helpful to work on a *nix type of platform. Some people seem to be successful with Windows especially when using the Windows Bash Shell - but I can’t help shaking the impression that Windows increases the amount of friction you have to deal with.
• Seems people like to use vscode-elixir-ls but your favourite text editor will do.