No, you cannot use the decoupling pin as a power supply.
What you can do is connect the 5V USB supply to VDDH and configure it to supply 3.3V to VDD. See also Regulator specifications, REG0 stage.
Are you mean 5V USB supply to VDDH,then the VDD voltate can be configured to 3.3V, then I can use this 3.3V as a power supply for sensor or MCU?
I see the VDD output can be configured to 3.3V, now my question is can I use this 3.3V as a power supply for external sensor and MCU?
Yes, as long as you adhere to Regulator specifications, REG0 stage.
