You have no privacy from Discord Inc. They can read everything if they want to:
>investigation is centered around the reported messages, but can expand if the evidence shows that there’s a bigger violation.
>we may investigate whether the entire server is dedicated to bad behavior, or if the behavior appears to be part of a wider pattern.
>we know there is also violating content on Discord that might go unreported. This is where we get proactive.
>When we have data suggesting that a user is engaging in illegal activity or violating our policies, we investigate their networks, activity on Discord, and their messages to proactively detect accomplices and determine whether violations have occurred.
https://discord.com/safety/360043712132-how-we-investigate