To enable the GPIO clock, you have to toggle bit 8 in RESETS_RESET (PADS_BANK0). Block diagram of an RP2040 GPIO pad. That figured out, I looked at the GPIO peripheral section in the documentation ...

The latest Pico-SDK includes many new features, including certification for 200 MHz clock speeds for the RP2040. Boards designed around the Raspberry Pi 2040 microcontroller can now officially be ...