In the meantime, I found out with an offline test installation that the error is related to the PHP version used. In the live installation, PHP 8.1 is activated by the provider. In my virtual environment I installed PHP 8.0 – and the upload works fine there.
So my new question is: What can be done to ensure that this great extension can also be used under PHP 8.1, or when will a corresponding update for PHP 8.1 be released?
Please support/help.
Thanks very much