Decentralized

Groups only exist on members' smartphones. Threema itself cannot see who is a member of a group or what the group is called. Groups can contain up to 256 members.

See also here:

https://threema.ch/en/faq/groupchat

And with Threema, the groups at least work reliably. Every message is there in a second . In contrast to SimplexChat, where the groups are no longer usable after 30 or 40 people because messages only arrive a day later!