The EN pin exposed on the headers of some Unexpected Maker boards, is tied to the 3V3 LDO on the board. When the pin is pulled LOW (pulled to GND) it shuts down the LDO, which in tun shuts down the 3V3 power rail and anything connected to it, like the ESP32 chip.
By default, the EN pin is pulled HIGH, which enables the LDO.
In the case of boards that have 2 3V3 LDOs, it is tied to the first “main” LDO.
The following Unexpected Maker development boards have an EN pin exposed on the headers: