Matrix is probably the best replacement for Discord if you leverage the Community and persistent room features.

Trouble is : Discord *organizes* things sooooooooo much better.

Matrix is also a huge PITA to self-host properly.

Discord is a *really good choice*.

I like FOSS to a dangerous level but hot damn @maloki has done a fantastic job structuring their discord and I just can't find a good way to make a FOSS solution as robust. I can get reasonably close but not 100%.