Shelly Uni - Compatible with HC-SR04 (ultrasonic water sensor) - anyone know?

In theory you could get it to work but the circuit gives back a pulse (indication of proximity ) that is extremly short (150 us- 25 msec ) and you need to measure it to get the distance - with current firmware of the UNI you can't do this in an accurate way. A solution could be to do the measurement via arduino and send the result to to UNI via analog signal - maybe not the easiest solution

Another solution could be to get a module that gives a constant analog output based on proximity.