Use the BOOT button on ESP boards as a regular input.

boot_button_as_input.py

# After booting, the BOOT button attached to GPIO 0 is available to use as a regular input for your program.
# GPIO 9 is used for BOOT on the ESP32-C3. Check the Espressif docs for other ESP variations.
from machine import Pin

p0 = Pin(0, Pin.IN, Pin.PULL_UP)  # Normal state is logic high, pressing the button will pull it low.
pressed = False  # Flag to track if button was pressed.

def irq_handler(pin):
    global pressed
    pressed = True

p0.irq(trigger=Pin.IRQ_FALLING, handler=irq_handler)  # Trigger on high to low (falling) level transition.

while True:
    if (pressed == True):
        print('Button press detected.')
        # Do something useful here.
        pressed = False  # Clear the flag to be ready for the next press.