I created a custom notification system that notifies me about certain keywords in certain channels. Not even visiting discord, just receiving notifications by email.
You don't have to control anything. All the data is delivered to your browser in a form of push notifications. Read them programmatically, filter and send yourself an email.
I don't think this can fall to definition of a "discord bot" at all. It certainly doesn't violate anyones' ToS.
And yea I know client modifications haven't been allowed in years, although they haven't really cracked down on it much aside from completely separate third party clients.