The reason why the network speed will become very slow after connecting the Bluetooth headset is that many mobile phones are single-antenna design, that is, Bluetooth and wireless network share an antenna, which leads to the interference of Bluetooth signal and wireless network signal, resulting in a slow network or even no signal.
There is also a case that the Bluetooth signal interferes with the wireless network signal, and the wireless network frequency band and the Bluetooth transmission frequency band coincide, causing the two signals to interfere with each other. In this case, you can try to enter the router to change the band bandwidth.