$array = [
'a' => 'abc',
'aa' => 'abc',
'aaa' => 'abc',
'b' => 'bbc',
'c' => 'cbc',
'd' => 123,
1 => '123',
2 => 123
];
$arr = array_keys($array,'123',false);
echo '';
print_r($arr);
result:
array
(
[0] => d
[1] => 1
[2] => 2
)