Found some answers:
https://www.reddit.com/r/esp32/comments/et1s50/confused_by_io16_on_esp32cam/?sort=top
-> same issue, but no solution :-(

https://rntlab.com/question/espcam-gpio-16-not-available/
-> similar issue, but seems to be due to 10k pullup, rather than sourcing high the GPIO16 (as ...

Without pulldown, the voltage would be 3.2 V due to the pullup resistor in the ESP32CAM board.
In my case it has an additional purpose, I setup a voltage divider for the 5V output voltage of the Arduino RS232 TxD I want to receive using the ESP32 RxD2.

Do you know, if PSRAM is enabled by Arduino ...

Hello,

on my ESP32CAM board (two different boards tested), the GPIO16 pin (RXD2) is stuck to high.
22 kOhm resistor connected to ground (to make voltage divider with the on board 10 kOhm pullup).
After SW was flashed the pin shows ~2.2 V.
After I perform a reset (reset-button)
the measured voltage ...