You'll want to be aware of these;
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Dragon Heist
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Dungeon of the Mad Mage
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Ultimate Undermountain
And as Mr. Z indicates, The names Waterdeep, Undermountain, Halaster, etc are copyrighted. So the only place you can distribute content you make relative to Waterdeep and Undermountain is through the DMsGuild.com and making sure you are in compliance with the CCA of that site.
Given that I'm the lead author on Ultimate Undermountain, let me know if you have questions on what it would take to get your stuff on the Guild.