There's a red "1" notification on the Settings button at the bottom right, but I have no idea what it is.
Clicking on the button just opens Settings, no markings saying what the notification is related to.
Poking around a couple of settings didn't reveal anything.
On Android, v2.24.0
FIXED - It was a notification that an upgrade was available.
Try upgrading, it should be fixed recently!
Indeed, the next time I reloaded the app, it was automagically updated to v2.24.2, and the red notification was gone.