How do you detect how many messages a user has using the Discord API or other methods? (You would have the user’s token.)

I looked at the api already, didn’t see any specific ways.

If someone pinged me, the number would go up by 1. If I read the message, it would go down by 1.
The Scratch API has and endpoint for this https://api.scratch.mit.edu/users/The_Mad_Punter/messages/count
and I want the same general output.