I am discussing with the AA6KL9 to build a new firmware using the STM32F303CCT6. If all goes well, it can be provided later. To replace the mcu directly on the current hardware, you need to add a 1.5K resistor to the VCC on the USBDP Pin. The DFU mode of the STM32F303 requires an external 8M crystal to use USB, but STM32F072 does not need it, so you need to use SWD to update the firmware. You need to prepare an ST-Link or DAP-Link.
BTW: The new STM32F072-based NanoVNA firmware already supports TDR.
Thank you!
