I just hit one of the little Big Sur annoyances: Up until Catalina, it was very easy to check the battery levels of your Bluetooth peripherals. You clicked on the little Menubar Bluetooth logo, select the peripheral, and had that information at the ready. In Big Sur, you apparently only see the battery level when you're charging the peripheral.
Why on earth would you do that? The information is valuable. I periodically check in to see if I need to charge something, for instance, the trackpad that came with the computer and has no frickin power level indicator on the device. I dunno, maybe I'm the weirdo here. It doesn't take up any space, because you have to click on the icon to reveal it in the first place. That's the whole point of menus! Does the person who designed this thing even use a Mac?!