Apple has released a new firmware update (2A36) designed for its AirTag trackers. There’s no release notes on what the update involves.
You can’t force an AirTag update, as it’s something that’s done over-the-air through a connected iPhone. To make sure the update happens, you can put your AirTag in range of your iPhone, but you have to wait for the firmware to roll out to your device. You can check your current AirTag firmware version through the Find My app, with instructions available in this how-to.