Solution: Repeat each number

Here is a possible solution to the task.

Code

my @result = gather for 1..4 -> $n {
    take $n for 1..$n;
};

say @result;

🦋 You can find the source code in the file collect-the-evens.raku.

[1 2 2 3 3 3 4 4 4 4]

Nothing forces a single take per iteration. Here the inner take $n for 1..$n runs take a different number of times on each pass, which is exactly the flexibility that makes gather/take more powerful than a plain map.
The outer loop uses a named variable -> $n on purpose. If we wrote the inner loop with $_, the inner for would rebind $_ to its own counter, and we would take the counter instead of the current number.
gather simply collects every value that was taken, in order, so @result ends up holding 1, then two 2s, then three 3s, then four 4s.