Here's the code I use to set up the interrupt:

// Enable acc interrupt
  buf = 1<<1;
  M5.IMU.I2C_Write_NBytes(SH200I_ADDRESS, 0x14, 1, &buf);

  // Set acc threshold
  buf = 100;
  M5.IMU.I2C_Write_NBytes(SH200I_ADDRESS, 0x17, 1, &buf);
  
  // Set amount of time acc must be in threshold before interrupt is triggered
  buf = 4;
  M5.IMU.I2C_Write_NBytes(SH200I_ADDRESS, 0x19, 1, &buf);

  // set gyro x/y/z as inputs for interrupt (bit 7 enables the use of TIME_THRESHOLD)
  buf = 1<<4 | 1<<5 | 1<<6 | 1<<7;
  M5.IMU.I2C_Write_NBytes(SH200I_ADDRESS, 0x1B, 1, &buf);

And this is the line that should enable wake on GPIO35 activity:
esp_sleep_enable_ext0_wakeup((gpio_num_t)35, 1); // set ext0 to wake up when GPIO35 is high

I've also tried enabling wakeup on one of the external M5Stick buttons as a sanity check.. that worked fine.

My question; is the SH200Q's interrupt actually hooked up to anything, and if so what? Or is there some error in my code?