Welcome to Elixir community @Konbor704, the problem here is that this code is trying to calculate 4 million fibonacci numbers, NOT fibonacci numbers less than 4_000_000.
See this line:

fib_numbers = Fibonacci.fibonacci_do(limit)

So, your Elixir program is doing a long computation because Fibonacci numbers tend to grow very fast.

If you want to calculate fibonacci numbers, you can use the Stream and Enum modules, specifically look at Stream.unfold:

# This one-liner creates an infinite "list" of numbers from
# which you can extract as many numbers as you want.
# The elements will be calculated on-demand by calling
# the passed function
Stream.unfold({0, 1}, fn {a, b} -> {a, {b, a + b}} end)

Now if you want the first 100 Fibonacci numbers, you can do:

Stream.unfold({0, 1}, fn {a, b} -> {a, {b, a + b}} end)
|> Enum.take(100)

If you want all fibonacci numbers less than 4 million, you can do:

Stream.unfold({0, 1}, fn {a, b} -> {a, {b, a + b}} end)
|> Enum.take_while(fn number -> number < 4_000_000 end)

Further, if you want to sum the numbers, you can pipe the above output to Enum.sum.

Enjoy learning Elixir and have fun solving problems.

EDIT: I would also suggest looking at the Elixir pipe operator ( |> operator). It is one of the most loved features of Elixir and you’ll soon find out how you can improve your code to make it more readable and how it also helps to understand the parameter positions for a function in a given module (thus allowing you to easily understand and making it easier to memorize standard library module functions!)

Thank you so much for explanation.