ESP32-S2 WROOM Module with PCB Antenna - 4 MB flash and no PSRAM [4MB Flash] : ID 4919 : $3.25 : Adafruit Industries, Unique & fun DIY electronics and kits
ESP32: Using the Internal Flash File System – Tech Blog
ESP32: Writing and Reading from Internal Flash Memory (EEPROM) - YouTube
ESP32 Flash Memory - Save Permanent Data | Random Nerd Tutorials
Getting Started with Espressif ESP32 Wi-Fi & Bluetooth SoC using DOIT-ESP32-DevKit-V1 Development Board - CIRCUITSTATE Electronics