Does anyone care to share an example of the OrderService that is not anemic?
What you should end up with are plain OOPy objects that mirror the real world. They're not skewed or constrained by their database model. They shouldn't have any dependencies on your infrastructure layer. The object should encapsulate state, behaviour, validity and consistency.
An example (which is probably overkill) would be https://learn.microsoft.com/en-us/dotnet/architecture/micros...
The next post is about modelling an actor and it might provide more insight for you.
If you work this back to DDD, then the Order entity would have an AddOrderLine method. The central service would be responsible for handing out Order entities and saving them once modified.
Up until a few years ago (prior to my previous job) I was a hypothetical believer in DDD and actors as two equally viable alternatives. I am now strongly against DDD, but still agree with the article on a hypothetical basis about actors.
Ultimately DDD attempts to create real-world analogies in code; you know, dog inherits from pet inherits from mammal etc. In my opinion, this approach to OOP easily ends up creating code that is difficult to reason about. Probably because real-world things often have many responsibilities. Code becomes especially confusing when you have dozens of methods on domain objects that interact across several domains: the system-wide control flow becomes extremely complex. Now add outlier code/hacks, likely written to meet an unrealistic deadlines, and things rapidly become completely incomprehensible.
And there's more that's hard to put to words. I code for the love of it, and I truly hated every moment working in DDD code. That was I completely novel experience for me: I'm fine with boring work (it has to happen), but DDD just hit very differently.
For example if I'm building a pharmacy system a prescription means something to a patient, but also means something different (but similar) to a fulfillment team member. The prescription might have a prescriber, and its important for the patient to know the name, address and contact information of the prescriber. But for fullfulment purposes I don't care about the address or phone number, just the NPI, full name and title for labeling purposes. This doesn't just extend to data, but to actions, a patient can't "ship" a prescription and fullfulment can't "renew" a prescription. In a DDD model these should be two separate objects.