That would depend on how you installed it.

If you subscribed to it on Steam Workshop, go to that page to Unsubscribe.

If you installed it using NIT, that will uninstall it, too.

If you installed it manually, have a look at the download package (download it again if necessary). Notice which files go in each subfolder. Remove those files from the corresponding subfolders in Documents.

You might prefer to move the files to a new folder, on a path that NWN doesn't use, to make it easier to reinstall again later.

Actually, for most purposes, it's sufficient to remove the mod's files from the override folder. That's the one that changes the behaviour of all modules.

If it is a module, it will still show up in the Other Modules list for new games, unless you remove it from the modules folder. The other folders typically have no impact on any other modules, so leaving stuff in them does no harm, although removing junk is arguably best practice.

There is a list of subfolders here:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1309774090