Nintendo 64 flash cart using a Raspberry Pi Pico / RP2040 (USB Type-C connector). It can boot and run homebrew software with some limitations. Features such as support for up to 16MB ROMs, EEPROM emulation, and others are not available. 16M chip store firmware and roms. So, it only can run less than 16MB roms.
Please select option NTSC or PAL. Then picocart64 come with that firmware and testrom installed. You can test it directly when it come.

* USB type-C cable NOT include.
Source and UF2 Builder