https://discord.com/terms#5 is pretty permissive

Your content is yours, but you give us a license to it when you use Discord. Your content may be protected by certain intellectual property rights. We don’t own those. But by using our services, you grant us a license—which is a form of permission—to do the following with your content, in accordance with applicable legal requirements, in connection with operating, developing, and improving our services:

Use, copy, store, distribute, and communicate your content in manners consistent with your use of the services. (For example, so we can store and display your content.)
Publish, publicly perform, or publicly display your content if you’ve chosen to make it visible to others. (For example, so we can display your messages if you post them in certain servers or recommend that content to others.)
Monitor, modify, translate, and reformat your content. (For example, so we can resize an image you post to fit on a mobile device.)
Sublicense your content, to allow our services to work as intended. (For example, so we can store your content with our cloud service providers.)