Bots are often added to groups; by default, a bot with privacy mode enabled will not receive all messages, but only messages that meet these conditions:

• Commands starting with the forward slash character "/"
• Messages containing @mention of the bot
• Replies to bot messages
• Service messages (about adding a user, changing the group image, etc.)

Privacy mode is enabled by default in all bots. It can be turned off and in this case the bot will start receiving all messages, like any user of the group. All members of the group will see the current status of the privacy mode in the list of members.

To change the privacy mode, you need to write /setprivacy in BotFather and select the bot you want to change the privacy mode

If you want the bot to be able to read all messages in the group, you need to turn it off (DISABLE)