Thanks Piranha, apologies I took some shortcuts in my message.The OP is using Sleep mode, I'm having the same problem (RTC internal wake-up doesn't wake-up STM32U5) in Stop mode. In my case what solved the issue was to add a call to HAL_DBGMCU_Enable...

In my case, I was missing the call to:HAL_DBGMCU_EnableDBGStandbyMode();By adding that, the RTC internal wake-up started to work.Any idea as to why though? I don't think that should be enabled during sleep, because according to the Reference Manual:"...