What is com.apple.MobileSoftwareUpdate.UpdateBrainService doing?

What is com.apple.MobileSoftwareUpdate.UpdateBrainService? I have it running and using a lot of CPU resources. (about 300% CPU core in top) I also found out it would mount a partition at /System/Volumes/Update/mnt1 when it's running. I am not 100% sure if this mount point is related to this process. It's just my observation. I am running MacOS Big Sur 11.2.3 (20D91). My auto update is always turned **off**. I found two online links talking about it, [link1](https://discussions.apple.com/thread/252177683) and [link2](https://www.reddit.com/r/MacOS/comments/lhhrb9/what_is/) . But they don't explain what it is and why it's running. Thank you very much. **Update 1:** I figured out even if I have Automatically keep my Mac up to date turned off. There is an Advanced... button in **Software Update** preference. In the Advanced... setup popup window, it has the following options enabled: Check for updates, Download new updates when available. I think this might cause com.apple.MobileSoftwareUpdate.UpdateBrainService process running and downloaded Big Sur updates. I am not very sure. Just a guess. **Update 2:** I have clicked **Restart** in ***Software Update*** preference. Now, my system updated to 11.4. I have turned off Check for updates in Advanced... window. Hopefully, this issue and process will never run again.