Raspberry PI SBCs run a deamon, ppdd, that listens for I²C events on the Pi's secondary I²C bus using pigpiod, with the RPi Pico (or most any CircuitPython capable MCU board) as I²C controller and the RPi as I²C peripheral.
One of the connected RPi is designated as primary ('bosmang'), and can send control commands & requests for stats to any other connected RPi. A command line tool, ppcc, is used for this and may be scripted like any other Linux system program. Alternatively, hardware connected to the RPi Pico (sensors, buttons, LEDs, displays, etc.) can trigger control signals to connected RPi devices & display stats from connected RPi devices.