Bookly support wasn’t much help, despite multiple support requests and a few explanatory emails, their only solution was: Install a third-party plugin to replace the plugins wp-autoupdate that isn’t available by default, or at least can’t be activated all the time (can only be activated if a new plugin update is currently available).
The support team tries hard but is actually quite incompetent to solve the issue.
I will think carefully about whether I use the plugin again for professional purposes, it took more effort than is to be expected from a premium plugin.