I don't remember an alternative. All FOSS are just based on Matrix or XMPP, and both are hard to call good choices. They're overcomplicated.

well, it is selfhosted, but only federated, so the server admin can still play a judge and remove accouts, etc.

Simplex.chat has great ambitions, but is very new. Element and matrix is super mature in comparison.

Also with simplex you can not have one account logged in on multiple devices, with matrix/element you can.