I was recently referred to the list in the following article. It's good information, even though it doesn't include the full scoop on 34-39.
ESP32 Pinout Reference: Which GPIO pins should you use? | Random Nerd Tutorials
Use anything marked 'ok' without notation (GPIO13, 16-33) .
34-39 are useable, if not as outputs - or in the carefree, Arduino sense of "useable".