Why is the server still in the community when I enabled Modded in oxide.com fig.json and restarted the server three times?

I'm not exactly sure, but you can try to type "oxide.version" in the server/rcon console when the server is running. Then, if you can't see info about the current oxide version installed on the server, that means it's entirely vanilla despite the fact that you might have an oxide folder and plugins from previous startups. You'll have to properly install oxide in order to load the plugins and switch to the modded tab. Apart from this, I have no idea what else can cause the server to be in the community tab if the oxide is installed and updated and it's set to modded - true.