Hi Balázs,
Please deactivate the premium plugin and then update the basic plugin.
Now, download the latest premium version from here.
And manually update the plugin like the following tutorial:
https://www.youtube.com/watch?v=anzv8IsiP2o&ab_channel=GetWooPlugins
Let me know if the problem is resolved.
Thank You
update
Balázs Kovács
First, I update the free version and the whole webshop falls apart. It still works fine with version 2.0.9