ForumChannel is a forum or media channel: it only contains posts, which are threads. It is what channel.isForum() gives.
A post is a
ThreadChannel: send its messages, archive it or change its tags there. The first message of a post takes everything of Sending messages.Properties
It also has everything of GuildChannel. Messages can’t be sent in the forum itself, only in its posts.The tags posts of this forum can have. Each entry is a
ForumTag.Actions
createPost()
ForumPostOptions.
Discord documentation