Arduino Edge Control: https://www.arduino.cc/pro/hardware/product/edge-control
It is a nRF52840 processor, running at 64 MHz.
The I2C bus should work of course.
As far as I can tell from the schematic, the I2C bus is only available on both MKR headers. There is no need to power the MKR modules, since the I2C bus is directly connected to the processor.
Both the pullup resistors and the expander are powered via a gated 3.3V controlled by GPIO46. I assume that enabling the 3.3V and 5V is enough to make it work.
What makes you think that the I2C bus does not work ?
There are already 10k pullup resistors on the board, and there is a I2C expander on the board. So if you run a I2C scanner, then it should find the expander.
You could do Wire.begin() in setup() and measure the SDA and SCL pins. The voltage should be near 3.3V. You could even measure the shortcut current of SDA to GND and of SCL to GND and you should be able to verify the 10k pullup resistors from the current.
[EDIT] Fixed link to datasheet.