Projects in MicroPython and on the Rasbperry Pi Pico (RP2040). P stands for Pure Python projects, to complete these you don't need anything except a few LEDs and for many of them you only need the Pico alone or an RP2040 with a serial connection.
S are System-level projects. These projects might involve low-level programming, interacting directly with hardware, or integrating with operating systems.