Is drupal/embed a dependency, or not?

I am taking this one over.

I had the same issue, and created MR for that.

DRD doesn't require the embed module. That must be caused by something else, but not DRD. So, adding the embed module would probably prevent the symptom on that one particular website, but we can't enforce that extra module on all users, as this is not happening elsewhere.

Instead, we need to find out, why this is happening on that one particular site. More details on when exactly that's happening and also a stack trace would certainly be good starting points for the analysis.