After I tried to update the database I got the following error:
[error] The "pdf_thumbnail" plugin does not exist. in Drupal\Core\Plugin\DefaultPluginManager->doGetDefinition() (line 52 of /home/www/sites/stdev/web/core/lib/Drupal/Component/Plugin/Discovery/DiscoveryTrait.php).
I tried to find the solution and found one of a similar issue:
Alas, I can't apply that solution because I don't know which module uses the pdf_thumbnail plugin. How can I find it out which module uses the plugin and solve the problem with the update?