This symbol is related to syncing between devices. I noticed it after updating to 18.2.1 on my iPad. I also have an iPhone but haven’t updated it yet. After checking “Screen Time” under “Settings”, I noticed that it was showing the use of “Apps and Website Activity” of both devices.
I listen to Podcasts on my iPhone but not on my iPad. I also use YouTube on my iPad but not on my iPhone. When I view “Screen Time”, it shows data from All Devices, but I can toggle on and off to view my screen time on each synched devices.
So, this new symbol shows that data is being synced between these two devices and even though I haven’t yet updated my iPhone and it doesn’t have the new symbol, I can see the exact use of data on both. I’m fairly certain that this new symbol will show up on my iPhone if and when I update to 18.2.1
This syncing also occurs even if both devices are not connected to each other by Bluetooth or Hotspot.