In case somebody chances across this in the future, I had someone help incorporate the library from M5Stack:
Instructions for the RFID2 and Ultrasonic I2C RCWL-9620 should now be good there. Tested both, confirmed working well on an Atom Lite and a PoESP32 device
Thank you! Worked out of the box for me. Very helpful.
I use a ESP32 DevKit and HC-SR04 (RCWL-9610 design) from eBay (HC-SR04)
This one can work in 4 different modes: GPIO, IIC, UART and OneWire. I needed IIC and it works fine!