<?php

$tagged_fruits = [
    [
        '11' => 'apple',
        '12' => 'banana',
        '13' => 'cherry',
    ],
    [
        '14' => 'pear',
        '15' => 'apricot',
        '16' => 'plum',
    ],
    [
        '17' => 'grapes',
        '18' => 'peach',
        '19' => 'melon',
    ],
    [
        '20' => 'strawberry',
    ],
];

$foreach = [];
foreach($tagged_fruits as $fruits) {
    foreach($fruits as $id => $fruit) {
        $foreach[$id] = $fruit;
    }
}

$walked = [];
\array_walk($tagged_fruits, function ($fruits) use (&$walked) {
    $walked += $fruits;
});

\var_dump([
    'tagged' => $tagged_fruits,
    'merged' => \array_merge(...$tagged_fruits),
    'walked' => $walked,
    'reduced' => \array_reduce($tagged_fruits, function($reduced, $fruits){
        $reduced = is_array($reduced) ? ($reduced + $fruits) : $fruits;

        return $reduced;
    }),
    'recursive' => \array_merge_recursive(...$tagged_fruits),
    'foreach' => $foreach,
]);