You are right. After a bit of research I discovered that my board as a wrong serygraphy for that pin.
As you say that pin is the CMD pin.
Thank you for the help

Ok, after some serious headache I got it.
If I take the ground on the GND-pin near 5v I get all those strange measurement, but if I take it in the other side of the board i get the full volts I'm expecting.
Do you have some explanation of this behavior?
P.S this happens on both board I have

I mean that it doesn't restart, it prints out the things that it has to print, it has no problem except that low voltage thing.
I get the same lectures (1.8v on 5v pin and 0.4v on 3.3v pin) whit hello word and after i erased the board.
Now i'm going to buy a new one, and check if the problem is ...

Ok, I both erased and flashed idf hello_word in the board, but I get the same results. In the console there isn't any reboot.
I tried to power the esp32 with a PC port and a wall adapter with 2 ampere, but nothing changed. However programs run flawlessly.

OH yes, that was an experimental change to find a solution . If I put the gpio as OUTPUT i get the same results

Hi,
I was trying to power a simple led, but when I set the output high it flickered. So i measured the voltage whit an external multimeter and it said 0.3v! So I tested the voltage on 5v and it was 1.8, on 3.3v was 0.3.

Despite this the board was in softAP mode and communicating with the computer ...