Remark, that calculations on date are not defined as bijective operations. The Summertime is integrated by mixing two concepts. You should test it beforehead.
Datetime will correct a date after each summation, if a date (29.2.2021 => 1.3.2021) or a datetime (29.3.2020 2:30 am (Europe/Berlin) => 29.3.2020 3:30 or 29.3.2020 1:30)
Example
<?php
$expectEaster = date_create_from_format('Y-m-d H:i:s', '2020-04-12 12:00:00', new DateTimeZone('Europe/Berlin'));
$interval = new DateInterval('PT20761M');
$expectEaster->sub($interval);
echo('recalc '.$expectEaster->format('Y-m-d H:i:s')."\n");
$expectEaster->add($interval);
echo('easter '.$expectEaster->format('Y-m-d H:i:s')."\n" );
$expectEaster = date_create_from_format('Y-m-d H:i:s', '2020-04-12 12:00:00', new DateTimeZone('Europe/Berlin'));
$interval = new DateInterval('PT20760M');
$expectEaster->sub($interval);
echo('recalc '.$expectEaster->format('Y-m-d H:i:s')."\n");
$expectEaster->add($interval);
echo('easter '.$expectEaster->format('Y-m-d H:i:s')."\n");
$expectEaster = date_create_from_format('Y-m-d H:i:s', '2020-04-12 12:00:00', new DateTimeZone('Europe/Berlin'));
$interval = new DateInterval('PT20701M');
$expectEaster->sub($interval);
echo('recalc '.$expectEaster->format('Y-m-d H:i:s')."\n");
$expectEaster->add($interval);
echo('easter '.$expectEaster->format('Y-m-d H:i:s')."\n");
$expectEaster = date_create_from_format('Y-m-d H:i:s', '2020-04-12 12:00:00', new DateTimeZone('Europe/Berlin'));
$interval = new DateInterval('PT20700M');
$expectEaster->sub($interval);
echo('recalc '.$expectEaster->format('Y-m-d H:i:s')."\n");
$expectEaster->add($interval);
echo('easter '.$expectEaster->format('Y-m-d H:i:s')."\n");