The Buzz has a built-in video transmitter (VTX) cutoff, which can save your VTX from overheating when the drone is sitting stationary. By default, the VTX cutoff function is set on Aux 4. Basically, whichever switch on your transmitter is set for Aux 4 will turn the VTX on/off. If it is off, you will get no video or extremely short video range. Your Buzz and its VTX are not defective, you just need to turn the VTX on via Aux 4.

The VTX cutoff function is PWM based and is similar to (but does not work exactly like) pit mode, Real Pit, etc. The VTX cutoff (or what position it is currently in) will not show in the On-Screen Display (OSD) or Smart Audio menu. Moreover, it does not show up in the Modes tab as a switch either. Rather, it is built into the hardware with custom resource mapping.

Per the manual on page 9 (

If you are having video issues:

If you flashed the firmware to the Official Release of OmnibusF4 4.0.0, please remember to re-apply the factory/stock CLI ( settings so that the VTX cutoff function will work correctly.

Alternatively, your VTX may be turned off due to your transmitter setup. Check and set up any switch on Aux 4 and try again (low value is VTX off, and high value is VTX on, check in the Receiver tab of Betaflight Configurator).