The "concentrated mode" that appeared in iOS 15 is a function that temporarily blocks external information such as notifications that may reduce concentration and informs you later. When the centralized mode is turned on, the received notifications can be received at the specified time (notification summary), and the operation mode can be switched according to changes in usage conditions such as time and place (smart activation). More advanced operation is possible than "Good night mode".
When the centralized mode is enabled, the person who sent the message during that time will be notified of the status as "Mr. XX is not receiving notifications". That is the ability to "share centralized mode status", which is enabled by default.
Centralized mode status sharing acts as a kind of status feature for friends and acquaintances trying to reach you. Even if you send a message, you can not expect an immediate reply, and you can immediately judge that it seems that you will not be able to reply immediately because you are busy, so you will not be annoyed. In addition, privacy is maintained because the type of mode such as work / sleep is not notified.
Not limited to the message app, any app that supports centralized mode can share the centralized mode status. As of February 2022, there are only a few compatible third-party apps such as Slack, but it is expected to increase in the future.
In addition, there are switches that allow sharing of centralized mode status for each mode such as work and sleep. If you do not want to inform your friends / acquaintances, open the screen in the order of "Settings" → "Intensive mode" → "Mode name" → "Intensive mode status" and turn off the switch.