<?php declare(strict_types = 1);

/**
* @return array<string, mixed>
*/
function foo(): array
{
	// something from elsewhere (not in the scope of PHPStan)
	return [
                // removing or keeping those lines does/should not change the reporting
		'foo' => [
			'bar' => true,
		]
        ];
}

$data = foo();
$data = $data['foo'] ?? []; // <<< removing this line suppress the error
$data += [
	'default' => true,
];
foreach (['formatted'] as $field) {
	$data[$field] = empty($data[$field]) ? false : true;
}

$bar = $data['bar'];