hooli
As far as I'm aware what you are referring to as I also used a LOS device in the past is not available on GrapheneOS. Would definitely be awesome to have but I understand there are much bigger priorities then to add such a small UI change that not even everyone is going to benefit from especially with the limited resources the developers have.
Either way as @DeletedUser43 said there is a battery indicator in the quick settings that is displayed on the Bluetooth tile when a device is connected. I find it to be a very useful alternative especially if you have it in the first page of your quick settings tiles.
Also if you have multiple devices connected at once you can tap on the tile to get a overview of all of them.