As you can find from the respective reference manual (RM0451, RM0377, RM0367) section 6.3.10:
I/O states in Standby mode
In Standby mode, all I/O pins are high impedance except for:
• Reset pad
• Wakeup pins (WKUP1, WKUP2, WKUP3)
• RTC functions (tamper, time-stamp, RTC Alarm out, RTC clock calibration out) [...]
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Regards
/Peter
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