When thinking of sending a message in Discord, I have sometimes drafted messages in Emacs or Notepad. I'm afraid of fatfingering the message before I've finished writing it. If I write it somewhere else, there's no problem. I can copy and paste when I'm done.
I almost never send these messages.
It's funny because the messages themselves rarely ever need precision or care. It's often a quick update, or a room temperature take or reply. In context, nobody is likely to care a whole lot about a half-written message. At most I may be annoyed and up to a few people will be confused until I edit in the remainder or post a follow-up.
The better option is to write in the box. It's better because I can fatfinger it. Because accepting that risk means accepting that fatfingering is actually okay, that it's actually a workable situation. It's not actually a major problem of any sort. The situation is more than reparable. Writing in this way suggests a different habit. Instead of asking "what is the best approach?" I might ask, "if I don't send this now, when will I?" Leaning into that question can be helpful.
A nice thing about Discord over Slack in this context is that it doesn't have a drafts page. It doesn't encourage me to hold things back for later. The Android version even tends to forget what I've drafted in a channel if I don't send it for a while. (A day seems to be enough.)