LCD Display (20x2 DEM20231) - not even backlight :(

OK, your photos to start with.
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20181206_212055.jpg

20181206_212101.jpg

20181206_212052.jpg

I think you need a series resistor for the LED - try 220 Ohms for starters. Note that one row of the connector pins are the odd and the other row, the even numbers.