Go to https://qifi.org/, input your WiFi name and password, click generate and save the PNG. Open the .scad file in OpenSCAD and input the image name you saved and the text you want, render and export the resulting STL.

I printed this on a 0.4mm nozzle, inserted a filament change gcode on the layer where the background has ended printing and the QR code/letters starts. You need to print this with a light color on the bottom and a darker color on the top layers, otherwise it will not scan correctly.

Prefer scaling in the .scad file instead of in your slicer, as there is a hole in the back for hanging this on a wall.

You might need to change the font inside the .scad file as well, if you don't have the Ubuntu font installed. See Help -> Font List (inside OpenSCAD) for a list of fonts known to OpenSCAD.

Version 2: Fixed the QR code, as it was inverted on my print, and didn't scan. Lazy me didn't test-scan after rendering! Also made the QR code/letters/border extrusions smaller to avoid shadows messing up the QR code scanability.