Check especially the ground connection. Do not connect anything to the 3.3 volt pin. Did you see the note about the pullup resistor? I find picocom a lot simpler to use than screen.
The serial wires should be less than 50 cm long. If you need more distance to the PC, use a USB extension cable.
I don't know why, but now it works with a shortened cable and picocom. Letters are still crypted. Typing is possible, but sometimes letters are wrong and I have to correct them. Annoying.