It reads well to me, as someone familiar with Perl map and jq lambda. But I would syntactic sugar it rather more strongly using a new `|=>` operator implying a distributive `|>` into its now-inferred-and-silent => arguments:

    $result = $arr |> fn($x) |=>
        array_column($x, 'values'),
        array_merge(...$x),
        array_reduce($x, fn($carry, $item) => $carry + $item, 0),
        str_repeat('x', $x);

Of course, since I come from Perl, that lends itself well to cleaning up the array rollup in the middle using a reduce pipe, and then replacing all the words with operators to make incomprehensible gibberish but no longer needing to care about $x at all:

    $result = $arr |> $x:
        ||> 'values'
        |+< $i: $x + $i
        |> str_repeat('x', $x);

    $result = $arr |> $x: ||> 'values' |+< $i: $x + $i |> str_repeat('x', $x);

So. I wouldn’t necessarily implement everything I can see possible here, because Perl proved that the space of people willing to parse symbols rather than words is not the complete programmer space. But I do stand by the helpfulness of the switch-like |=> as defined above =)