That has the SAMD21G18A processor, which is quite complex, and not completely supported by any Arduino core that I've encountered.
Deep sleep is an extremely important but poorly supported function, especially with external interrupt wakeups. I've been struggling with that on and off for weeks now and unfortunately, the number of Arduino-oriented people who understand the SAMD21 well enough to help solve the sleep problem seems to be close to zero.
Libraries to try include the ArduinoLowPower, ZeroRTC and Adafruit SleepyDog libraries, but they all have issues, so study the (minimal) docs and try the examples.
Interrupt on state change may not work with any of them, because a separate clock for the external interrupt controller (EIC) has to be properly implemented and set up for each interrupt pin.
attachInterrupt(digitalPinToInterrupt(CLOCK_INTERRUPT_PIN), ISR, FALLING);
If you run into problems, carefully study the issues on the Github issue pages, as fixes are proposed that the library authors don't seem to be interested to implement.