So are you saying that your understanding is that what we write here on Lemmy is copyrighted, with authors holding the rights?

Yes, that's exactly it.

Services often do have:

you grant us a worldwide, non-exclusive, royalty-free license to use, reproduce, modify, adapt, publish, translate, distribute, and display such user content

But, I don't know how that plays out in different jurisdictions, which license those services redistribute the content as, and so on. That's for the copyright lawyers to figure out.

CC BY-NC-SA 4.0