arduino NANO33BLE output of digital pin

void setup() {
pinMode(9,OUTPUT);
}

void loop() {
digitalWrite(9,LOW);
}

I uploaded this program to Arduino NANO 33 BLE.
Then , I measured voltage between grand and 9pin.
I expected 3.3V.
But it was about 0.8V.
Please tell me why.

digitalWrite(9,HIGH);

thank you for pointing out .
I incorrectly typed "LOW "for the topic.

Actually, I uploaded "HIGH".

did you buy the version with soldered headers or did you solder the headers?

I bought the version with soldered headers.

and by pin 9 you mean the pin with while label 9 on the bottom of the PCB?

yes

and other pins?

I didn't connect other pin.

Why not?