Arduino for STM32

You need to poll the EWIF flag in loop() or use a timer based method. Here is a quick fix:
void loop() {
// Check early wakeup flag manually
if (LL_IWDG_IsActiveFlag_EWIF(IWDG)) {
Serial.println("Early Wakeup Interrupt Triggered!");
LL_IWDG_ClearFlag_EWIF(IWDG); // Clear the EWI flag ...