We’re rolling out end-to-end encryption for voice and video calls! We’d like to share why we’re bringing E2EE A/V to Discord, share our design and implementation goals, and provide a high-level technical overview of how it works.
It's weird that they're adding E2EE on voice but not in private text DMs, which is probably everybody's biggest concern when it comes to security on Discord. Better than nothing I guess.
Here is the article were they adjusted the privacy policy to allow AI training. Personally I think this is enough evidence to think they train their AI on messages.