Email cards shows correct time, Calendar does not

Question

I've got my Event Card approved and working. The card in Gmail shows the correct time (10pm Berlin, DE) but on the Google calendar it shows as 7am.

When I create the card I convert the date from Berlin to UTC and return the date in ISO 8601 format:

$dt = new \DateTime($dateString, new \DateTimeZone($this->timezone ?? \Phpr::$config->get('TIMEZONE')));
$dt->setTimezone(new \DateTimeZone("UTC"));

return $dt->format("c");

and this is the resulting markup:

<script type="application/ld+json">
    {
        "@context": "http://schema.org",
        "@type": "EventReservation",
        "reservationNumber": "2400071",
        "reservationStatus": "http://schema.org/Confirmed",
        "underName": {
            "@type": "Person",
            "name": "Some dude's name"
        },
        "reservationFor": {
            "@type": "Event",
            "name": "Demo Event Flux (1)",
            "startDate": "2022-05-07T22:00:00+10:00",
            "endDate": "2022-05-08T03:00:00+10:00",
            "url": "https://www.yyy.zzz/event/demo-event-fl-1",
            "location": {
                "@type": "Place",
                "name": "Berlin Central Station",
                "address": {
                    "@type": "PostalAddress",
                    "streetAddress": "Europaplatz 1",
                    "addressLocality": "Berlin",
                    "addressRegion": "Berlin",
                    "postalCode": "10557",
                    "addressCountry": "DE"
                }
            }
        }
    }
</script>

I'm not sure, but seems that this is a Calendar problem, not a schema problem. Maybe Calendar doesn't have enough information to know the precise timezone? Maybe my conversion is wrong.

Has this happened to you? Thanks