If you are curious as to when the internal array gets resetted (from https://onlinephp.io/c/3ee35):

<?php

$date0 = DateTimeImmutable::createFromFormat('!Y-m-d', '2020-31-31');
var_dump($date0->format('c')); // 2022-07-31T00:00:00+00:00

foreach(range(0,2) as $_)
    // The internal error won't reset
    var_dump( join(DateTimeImmutable::getLastErrors()['warnings']) ); // The parsed date was invalid
    
$date1 = DateTimeImmutable::createFromFormat('!Y-m-d', '2020-12-31');
var_dump($date1->format('c')); // 2020-12-31T00:00:00+00:00

// The internal error did reset
var_dump( empty(DateTimeImmutable::getLastErrors()['warnings']) ); // true

$date2 = DateTimeImmutable::createFromFormat('!Y-m-d', '2020-31-31');
var_dump( join(DateTimeImmutable::getLastErrors()['warnings']) ); // The parsed date was invalid
$date3 = new DateTimeImmutable('2023-12-31T00:00:00.000000Z');

// The internal error did reset
var_dump( empty(DateTimeImmutable::getLastErrors()['warnings']) ); // true
?>

Output:
string(25) "2022-07-31T00:00:00+00:00"
string(27) "The parsed date was invalid"
string(27) "The parsed date was invalid"
string(27) "The parsed date was invalid"
string(25) "2020-12-31T00:00:00+00:00"
bool(true)
string(27) "The parsed date was invalid"
bool(true)