Вот тута прямо пишут, что можно одну ногу подключить и к ADC и к
компаратору. Но предупреждают, что зарядка емкости УВХ может
вызвать срань на выходе компаратора. https://community.st.com/t5/stm32-mcus-products/sharing-inputs-between-adc-and-comparators-on-stm32f303/td-p/301594
https://electronics.stackexchange.com/questions/210292/stm32f0x1-comparator-comp-and-adc-on-same-pin-simultaneously
PS. В аппноте AN4232 прямо предлагают так делать
Moreover, the comparator input is an ADC channel so PCB designer does not need to make an external connection between the comparator input and the ADC channel. In an analog voltage monitoring application where the sensor output voltage is lower than the threshold, the MCU remains in Stop mode thereby saving power. As soon as the sensor output exceeds the threshold, the analog comparator wakes up the MCU, the ADC is powered on, and the analog input voltage is measured. When the sensor output is lower than the threshold, the MCU re-enters the low-power mode to save battery life. Enabling the ADC only when required (analog voltage higher than a threshold) dramatically reduces the average power consumption, as compared to an application where the ADC is always enabled whatever the analog voltage.