I submitted the fix to #8393 to expose pin 20 on ESP32. On the Adafruit Feather ESP32 V2, SCL is pin 20. I loaded the latest nightly build onto my board. I am running into the following issues.

When trying to initalise I2C, it is not accepting pin 20 as a viable option for SCL.

>>> from machine import Pin, I2C
>>> i2c = I2C(0, scl=Pin(20), sda=Pin(22))
E (2540280) i2c: /home/micropython/esp-idf-v4.2/components/driver/i2c.c:767 (i2c_set_pin):scl gpio number error

I2C set up works with pin 14 as SCL.

If I try to simply init pin 20 as an output, it also fails.

>>> from machine import Pin
>>> p20 = Pin(20, Pin.OUT)
E (19500) gpio: gpio_set_direction(263): GPIO number error

@jepler suggested that perhaps the issue is resolved in the ESP IDF v4.4, but an attempt to build MicroPython with that version resulted in a failure to fit in flash. So, I have not tested this possibility.