ESP32 JTAG Debugging can be done through a MicroSD Card Socket

Found in most microcontrollers and processors, JTAG is an industry standard for verifying designs and testing printed circuit boards after manufacture, and that is also often used for low-level debugging or reverse-engineering.

Espressif ESP32 also has a JTAG interface, but interestingly it's shared with the SD card interface, and in ESP32 LyRaT audio development board where both MicroSD card slot and JTAG header are present selection is made by jumpers.

The extract from ESP32 LyRaT schematics above shows IO's 12, 13, 14 and 15 can present on the SD card and 4-pin JTAG header. Some boards may not

The full article can be found @ https://www.cnx-software.com/2020/02/12/esp32-jtag-debugging-microsd-card-socket/