The PicoCPC use a Pico2, connected via multiplexor. This let enough pin to add an I2S DAC, MicroSD and some more control signals. Final PicoCPC will be with soldered RP2350B.
The board can decode any I/O port and of course RAM/ROM cycles. As it use a Pico2, its RAM is doubled vs Pico1 and it can access a 8MB PSRAM as well. Advantage of this model is on use of CH376 for USB : USB in FAT32&extfs, with nothing to do at the CPC side.
There is no external ROM, so the microntroller access the emulated RAM/ROM and USB/MicroUSB at the same time: Direct write from the uSD to the CPC emulated RAM at 3MB/s (For example).