How does one remove the fabia's rear wiper arm from its spindle?

it's only forced onto / press fit onto the splines by the retaining nut (same as front wipers), so remove the nut and then wiggle / apply penetrating lubricant and she should come off.

I have used a universal pulling tool.

You keep the nut on for leaverage. Do not apply force to the thread.

 

Oil and wriggling might work, but mind the spindle is part of the motor.

Be careful if you wiggle arm you can crack the screen, mine was solid but i found a £8 wiper puller on ebay and it came off easy using this puller a bit extreme but a new screen is a few hundred pounds for the sake of around £10 it's well worth buying one