STM32WLE5 compatibility

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Trying this library with STM32WLE5CCU6. In Arduino as far as i can tell the system is running on HSI at 48M, and the LSI is initialized by the core.
My board has HSE and LSE too.
Tried the following example, it never wakes.

#include "STM32LowPower.h"
#define DBG_TX PA9
#define DBG_RX PA10

void setup() {
  Serial.setTx(DBG_TX);
  Serial.setRx(DBG_RX);
  Serial.begin(115200);
  Serial.printf("init\n");
  delay(5);
  LowPower.begin();
}

void loop() {
  Serial.printf("sleep\n");
  delay(5);
  LowPower.deepSleep(5000);
  Serial.printf("wake\n");
  delay(5000);
}

init
sleep

Is the library simply not handling STM32WLE5 yet?

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On the other hand, shutdown(ms) works fine.