I tried this on a pyboard and it flashes the LED. Same program on the STM32L476_DISC port set the LED and freezes. Adapted it for the NUCLEO_F093RC and it also freezes.

Did anyone tested this functionality or can test this to confirm this behaviour?

import pyb
rtc = pyb.RTC()  # rtc is running

def lpdelay(ms):
    rtc.wakeup(ms)
    pyb.stop()
    rtc.wakeup(None)

led = pyb.LED(1)
while True:
    led.on()
    pyb.delay(1000)
    led.off()
    pyb.delay(1)
    lpdelay(1000)

For the NUCLEO_F093RC port using machine instead of pyb

import pyb, time, machine
rtc=pyb.RTC()

def lpdelay(ms):
    rtc.wakeup(ms)
    machine.sleep()
    rtc.wakeup(None)

led = pyb.LED(1)
while True:
    led.on()
    time.sleep_ms(1000)
    led.off()
    time.sleep_ms(1)
    lpdelay(1000)