NextcloudPi Preview Generator 64 Bit RaspberrypiOS


I hope somebody has a solution here, my problem is the following:

I’m using NextcloudPi in the newest version (1.39.1) and Nextcloud in 21.04.
The OS is RaspberryPi OS 64 bit on a RPi4 4GB. So far everything runs just fine with one problem: I can’t get the preview generator to do it’s work for HEIC Photos. Imagick is installed and # php -r ‘phpinfo();’ | grep HEIC shows that HEIC is available. I tried to rebuild the wohle preview cache, but it will only be generated for anything but HEIC. For older HEICs (I switched to the 64 bit system and restored a Nextcloud Backup) the previews were still available, but no new ones are generated.
So my question: Is there anything special that I have to configure, because it’s the 64 bit version of the OS? If not, what am I missing here? If you need anymore info I will try to add it as soon as possible.

Thanks in advance