Hi, when I try to use the serial port to download firmware through WCHISPTool, the device is not detected.

Proccess: 

I turn off the power, connect PB22 to GND, press the firmware download button in ISP, and turn the power back on.

 After this, you can see how the device gets into the system bootloader, and at this moment the starting sequence of the boot is sent via the serial port, however, the bootloader does not send anything in response, 10 seconds pass and the bootloader goes to the application without any result. 

USB booting works completely fine. All wires are connected correctly. Could this be a problem not on my side?

Solve the problem