Discord gives a notification for nitro promotional content that is similar to a friend request. I dislike this.

The notification appears in the same way that a friend request would, which leads people to look. In terms of marketing strategy, that is probably a very smart idea. But for the user, being tricked into looking at a promotion feels deceptive at best, and makes the notification system less reliable for things that might actually interest them. At minimum, changing this to at least be visibly different would help maintain trust in the systems in place. Ideally, there would be no notification for promotional content, but I understand why that would work against your company.