If fastboot is functioning correctly, there should be output from the UART serial console. However, video output or lcd won’t light up, which gives a illusion that the board isn’t booting. Also, a usb device will be detected if you connect the type-c OTG port to your computer, on which you can use fastboot uitility.
Also, as Loic just said. If there really is a problem, you can follow the recover procedure in the official doc.