These pins can be used as GPIOs.
It seems that the writer of the datasheet of ESP32-PICO-D4 forgot adding GPIO function to pin description

Using a efficient buck IC will help a lot. And what task you run may have a big impact for the battery life. You can measure the power consumption and the battery life by yourself. I think it's not too hard to operate.

GPIO2 should be low, when booting ESP32 in UART mode. Please check this point first.

I think the link below can answer your question:
https://www.instructables.com/id/Cleaning-up-your-PCB/

if you connect EXT 5V and USB VBUS directly, there will be current flowing between EXT 5V and USB, since the voltage levels of these two power supply may be different(e.g. EXT 5V is 5.1V, while USB VBUS is 4.8V). And this current may damage either EXT 5V or USB. You can add a diode for each the powe...

Hi jadhavashitoshj48,
For the relay drive circuit，
1. try to add a flywheel diode across the coil
2. try to add a RC Snubber between NO and COM

see more infomation here: https://www.electronics-tutorials.ws/bl ... rcuit.html

I think the schematic is OK, and you may check your code with respect to the GPIO init. You can post the code if you like. Also the GPIO may suffer noises from other part of the board. In this situation a larger value of the capacitor will help to solve the problem, e.g. 1uF.