read SD Card over SPI with Micropython. i run it with adafruit-ampy. maybe you need to place the sdcard module on the pico.

read.spi.py

import machine
import os
import sdcard
import uos
import sys
import ubinascii

# Setup SPI bus
spi = machine.SPI(0, sck=machine.Pin(2), mosi=machine.Pin(3), miso=machine.Pin(4))

# Setup SD card
sd = sdcard.SDCard(spi, machine.Pin(5))  # CS pin is GPIO 5

# Function to read a block
def read_block(block_num, block_size=512):
    block = bytearray(block_size)
    sd.readblocks(block_num, block)
    return block

# Main function to read and send data
def send_data_over_usb():
    block_count = sd.ioctl(4, 0)  # Get the total number of blocks

    for i in range(block_count):
        data = read_block(i)
        hex_data = ubinascii.hexlify(data).decode('utf-8')
        print(hex_data)

# Main function that runs on startup
def main():
    # Place your main code logic here
    # For example:
    send_data_over_usb()

if __name__ == '__main__':
    main()