Tabletop rules and settings are owned by their publishers. DMRealm deliberately does not copy their branding, their worlds, their signature monsters, or their art.
What it does include is reference material that is openly licensed for reuse — a large catalog of standard equipment, creatures, spells, and character options — with attribution kept where the licence requires it.
Why this is good for you
If you write a setting in DMRealm, it is yours. You can publish it, share it, and build on it without inheriting someone else's restrictions on what you are allowed to do with your own campaign.