Returning to what I wrote on July 12: finally, the modules to link the payment provider Mollie to Ubercart v4 are also finished. The first tests are showing promising results. This means that I can phase out Drupal 7 and use Drupal 8 for all sites, including the Bookshop. That comes in very handy, because it makes the link with dVU/CB a bit easier. Now just convert everything by hand 😞.