Add option to disable channel member list syncing

example-config.yaml

@@ -103,6 +103,10 @@ bridge:
     # will not send any more members.
     # Defaults to no local limit (-> limited to 10000 by server)
     max_initial_member_sync: -1
+    # Whether or not to sync the member list in channels.
+    # If no channel admins have logged into the bridge, the bridge won't be able to sync the member
+    # list regardless of this setting.
+    sync_channel_members: true
     # The maximum number of simultaneous Telegram deletions to handle.
     # A large number of simultaneous redactions could put strain on your homeserver.
     max_telegram_delete: 10

mautrix_telegram/config.py

@@ -185,6 +185,7 @@ class Config(DictWithRecursion):
         copy("bridge.bridge_notices")
         copy("bridge.bot_messages_as_notices")
         copy("bridge.max_initial_member_sync")
+        copy("bridge.sync_channel_members")
         copy("bridge.max_telegram_delete")
         copy("bridge.allow_matrix_login")
         copy("bridge.inline_images")

mautrix_telegram/portal.py

@@ -543,6 +543,9 @@ class Portal:
             chat = await user.client(GetFullChatRequest(chat_id=self.tgid))
             return chat.users, chat.full_chat.participants.participants
         elif self.peer_type == "channel":
+            if not self.megagroup and not config["bridge.sync_channel_members"]:
+                return [], []
+
             limit = config["bridge.max_initial_member_sync"]
             if limit == 0:
                 return [], []