rtc.h:136:24: error: 'RTC_LSECSS_IRQn' undeclared
The problem is that RTC_LSECSS_IRQn is declared only for M0 core of STM32WL55xx. M4 core has TAMP_STAMP_LSECSS_SSRU_IRQn also default decision to use RTC_WKUP_IRQn like it is commented now is acceptable.
The problem is that
RTC_LSECSS_IRQnis declared only for M0 core of STM32WL55xx. M4 core hasTAMP_STAMP_LSECSS_SSRU_IRQnalso default decision to useRTC_WKUP_IRQnlike it is commented now is acceptable.