I know Discord is super convenient and easy to use, but please don't use it for organizing purposes, this is a horrible idea for so many reasons. If you're going to use Discord for this purpose, you may as well just invite the local police officers to your meetings. This goes for Microsoft's Windows as well, but that's a whole different conversation and not in the scope of this post.

Piggybacking on what @hello_hello said, I'd bring Matrix to your organizations attention and lobby for it's adoption. It's free, open-source, decentralized/federated, and end-to-end encrypted (important!) and has everything you'd want like direct messages, group chats, voice & video calls, and plenty more.

If you really must use Discord, make a throw away e-mail that you only use on Discord, do not attach a phone number to your account, pick a username that you've never used on any other platform, don't talk about anything that could be linked back to you, etc. Assume everything you send/do is being looked at, because it is.