Signal version 5.22 introduces what it’s calling “announcement groups” and they work pretty similarly to the way they do in Telegram: admins are the only ones who can talk, and group calls are supported. Telegram broadcast groups restrict the ability for non-admins to talk while also allowing regular members to join live voice chats (note that a broadcast group is not the same thing as a channel). In WhatsApp, you can restrict non-admins from speaking in a group chat, so while broadcast groups aren’t an explicit feature, they can effectively be used; Signal is simply playing catch-up here.
In the end, Signal’s solution here works actually pretty similar to WhatsApp. You can create a regular group, and then disable permissions for non-admin users to send messages — then you got yourself an announcement group.
It may be a little before you can check it out, as this latest beta is not available in the Google Play Store just yet — be sure to join the beta program to get it first. If you want to try it out immediately, however, then you can either get it through Firebase App Delivery or download the APK right now from APKMirror.