This happens when the device enters a "mode-switch" state. In Linux, you may need to use usb_modeswitch to force it into Bluetooth mode.
In the rapidly evolving world of consumer electronics, two things determine the success of a smart audio device: the silicon inside it and the software that makes it sing. For years, original equipment manufacturers (ODMs) and audio enthusiasts have struggled with a fragmented market—chips that promise much but deliver little, paired with generic drivers that cause latency, dropouts, and compatibility nightmares. jieli br21 driver exclusive
The BR21 features rich GPIO capabilities. The "exclusive" part of the driver often involves the interrupt matrix. This happens when the device enters a "mode-switch" state