You can't connect your FC or BNF to the Betaflight Configurator?
Please check the instructions on the first startup screen of your Betaflight Configurator to approach that issue.
Did you probably run into a Driver issue?
For Windows machines, please try to use this Driver Fixer
https://impulserc.com/pages/downloads
When the drone is plugged into the USB, does the computer have the sound of identifying the device? Or check the computer driver to see if it recognizes the USB. If it is a MAC, you can try to use a USB hub to transfer
1. Change your computer, cable or if necessary reinstall drivers. There's no hardware defect if everything else works
Because not all usb cables are the same. some cables supply only power (charge cables) and no signal. checking the cable would be the best place to start
2. Please try to connect the USB first, and then connect the battery to see if it can connect the Betaflight normally.
You can also read this article to check if there any other wrong：
https://oscarliang.com/fc-driver-issues-flash-firmware/