That’s why with the launch of Pixel 4a (5G) and Pixel 5, Google introduced Adaptive Connectivity to ensure good battery life.
What it does? it automatically switches data from 5G to 4G, when high-speed operations are not carried out to save power automatically.
Therefore, with Android 12 Beta 1, we are able to see it on our Pixel phones as well.
There are more usage scenarios it kicks in like gaming, using Android Auto, etc.
However, Google has not shared how adaptive connectivity works in these situations.
Overall the basic use of this mode is to extend the battery life as much as possible.
Besides, you can find this option in ‘Network and internet’ settings from where you can enable it.