Raspberry Pi Pico Supported Peripherals
I2C peripherals
I2C peripherals like OLED Displays (e.g. SSD1306 or SH1106) and keyboards (e.g. CardKB) can be connected to GPIO pins 4 (SDA) and 5 (SCL), which will be recognized on boot. Note that for keyboard input, the Canned Message Module has to be enabled and the input source should be specified.
External device using Serial Module
For connecting an external device via the Serial Module, it's recommended to use GPIO pins 8 (serial.txd) and 9 (serial.rxd).