meta_query for an ACF checkbox field don’t works correctly

If you expecting a number as a value you can set the type parameter to NUMERIC.

Otherwise 0 is evaluated to false.

Then you can use IN comparison if you only want a set range.

$test_query = new WP_Query(
        [
            'meta_query' => [
                [
                    'key'     => 'test_key',
                    'value'   => [ 0, 1 ],
                    'compare' => 'IN',
                    'type'    => 'NUMERIC',
                ],
            ],
        ]
    );