NANO33 BLE pulseIn()?

pulseIn() does not appear to be supported on the nano 33 ble. what alternatives are there?

how about a hardware solution?

The nRF52840 has timers with capture function. You might need to do some datasheet reading and write your own functions and/or some google to find a ready solution.

Maybe this helps you get started:

https://devzone.nordicsemi.com/f/nordic-q-a/14097/how-to-use-the-timer-capture

https://devzone.nordicsemi.com/f/nordic-q-a/8707/how-to-use-timer1-capture-function