Imagine:
ESC32 have to sides: +5V for powering logical side and "lipo" connection for powering the motor.
If you solder "+5V" jumper (recommended) esc (logical side) is powered from separately +5V supply (e.g from FC)
For test make:
- main battery to points where you have capacitor
- +5V from UBEC to +5V ang GND pins
- connect to esc via GCS and make test with arm and start