The demo.py example should definitely show things up on the screen.
How does the soldering look on your Pico? Try running this:
import picoexplorer as explorer
width = explorer.get_width()
height = explorer.get_height()
display_buffer = bytearray(width * height * 2)
explorer.init(display_buffer)
explorer.set_pen(0,0,0)
explorer.clear()
explorer.set_pen(255,255,255)
explorer.text("Hello world!", 20, 20, 100, 4)
explorer.update()