Matrix?
matrix is a free, open source and decentralized messaging protocol. Basically, it's Discord if it was actually good security and privacy wise. The UI on the most used client is very similar and functions the same as Discord, so switching over shouldn't be too hard. The server is also hosted on MY hardware, so we don't have to trust and rely on some corporation for the service.
Using a client
Due to its open-source nature, there are many clients you can use to operate matrix. The one I recommend using (if you're new to matrix and used Discord before) is Element. You can get/use Element here, but don't do anything else without reading the next section first.
Setting it up
When greeted with the sign-in page, click sign in if I gave you an account login. If I decide to enable account creation, click sign up. This is important: make sure to set the home server to , not the default home server address (matrix.org). You should be able to figure the rest out, please note that on the first login it will take a while to load everything (due to encryption).