Trap for young players .. variation within the ESP32 Ecosphere - pinout Hell ..
Sure I am a n00b ..I make no assertion to the contrary.
As a Field Technician we fall into the habit of RTFM at mach 3 only on pieces of equipment we have never seen before. This until we have figured out how to get the covers off and then we never RTFM ever again.
I just dinged myself a half days down time over failures to upload across three different breeds of EPS Dev Boards on two prototype machines.
Only happens when the "breadboard" is actually hooked up - the sketches load just fine on the ESP by itself.
The errors are ..."MD5 flash mismatch" ... "header files not received" those kinda shenanigans ... smells like bad power.
Lots is said about power sag particularly running GPIO loads around the 30 mA range. Which I wasnt .. it was opto cuplers on a relay board. The entire board might have taken 30 x 4 mA with all the relays on but that wouldnt have gone near the guts of the board. And I tried it with the relays coils drivers isolated using the jumper.
Anyway as I say sometimes brevity can be a road to glory ... particularly when you are charging the customer an obscene hourly rate and, by the way, his whole factory is out of production till you get that fault vanquished.
In this instance however my problem was a failure to appreciate how subtle but chaotic the differences between the pinouts and the specs on these Dev Boards are.
Note to Self.... slow down and identify which exact ESP32 Dev you are working with and take time to verify the Documentation / Pinouts etc ... and don't expect them to be presented neatly or rationally or at all.