Not sure if you'd have to put an advertisement/thread in the servers section (https://www.minecraftforum.net/forums/servers-java-edition/pc-servers) even if it's for a build contest, otherwise if video or stream related to show your creations (https://www.minecraftforum.net/forums/show-your-creation/videos) then in that section most likely. I've not been to them that much or in your situation but that would be my guess.
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