Three sizes, and each trades features for reach.

Standard holds up to 256 people with every feature on. Large holds up to 1,024, with typing indicators, read receipts and presence shown in aggregate. Broadcast holds up to 10,000, and to do that it switches things off: only admins can post, reactions are disabled entirely, and typing, receipts and presence are all off.

So a broadcast group is right for announcements and wrong for discussion. If nobody can reply or react in your group, that is almost always why.