How about the complete schematic.
If you must use a higher-impedance divider/sensor, either add a small cap (≈0.1 µF) at the pin or buffer the signal. The ADC has a tiny sample/hold cap that must charge during a very short sampling window. With a 1–1.5 MΩ source it won’t settle, big, jittery errors. (It will “work” but readings wander, especially after channel switches or fast sampling.
Here are the official Espressif docs you’ll want:
ESP32 Hardware Design Guidelines (ADC section) – shows ADC pin mapping and the note to “add a 0.1 µF filter capacitor … when using the ADC” for better accuracy.
Espressif Documentation
ESP-FAQ: ADC explicitly states the ESP32 SAR-ADC sample-and-hold capacitance is ~1 pF (useful for source-impedance/sampling-settling).
Espressif Documentation
ESP32-WROOM-32E/32UE Datasheet – module datasheet with ADC characteristics and pin names (AIN0 = ADC1_CH0 on SENSOR_VP/GPIO36).
Espressif
ESP32 Technical Reference Manual – deep dive on the SAR-ADC block (architecture/timing).