How do you remove the key from the ignition of a 2005 Audi A6?

When your transmission is in park, it has a key release switch that can get corroded over time. I cleaned mine on my older Audi. You might be able to do that on yours.

If it is intermittent, run the lever from park to neutral, then back to park. Turn the key to start, but do not start the car. turn the key back to the off position. It should then pull out.