Is STM32 RTC halted during debug or not?
Found the solution: The STM32F411 have a register on the debug IP controlling the halted state of the RTC. Register is

Debug MCU APB1 freeze register (DBGMCU_APB1_FZ)

Reset state is 0. The field is

Bit 10 DBG_RTC_STOP: RTC stopped when Core is halted
0: The RTC counter clock continues even if the core is halted
1: The RTC counter clock is stopped when the core is halted

Reference manual p 830
My mistake was to not search in the debug IP part of the documentation but in the RTC part.