Plugin fullcalender google-ics german Umlaut not converted

Grav v1.7.35
Quark 2.0.4
Plugin FullCalendar v0.3.2
On the page named “Kalender” with the “Calendar” template, I have successfully imported/subscribed to a Google calendar using the shortcode [fullcalendar icsfile=“”]
[/fullcalendar]. Unfortunately, the German umlauts are not converted. So far I have not found a solution. Can anyone help me?

Has been extended by the plugin developer and now works perfectly. Thanks