The Via Kunig is an established route. Other potential routes between Ponferrada and Lugo are available to anyone who has a map and an inclination. The OP’s challenge is getting from Lugo to A Coruna by any possible route that doesn’t involve slogging the available road route. A decent mapping app, previously cited, will help but but I’m minded of the likely local response to any request for help and suggestions “por Que?”
If you’re on pilgrimage to the bones of Santiago why would you not simply walk to Santiago. And why would you not walk by the most direct route to those bones. Of course, if you’re just out for a stroll around Galicia then where you go and how you get there is entirely up to you.
A Coruna has been a major port for at least 1500 years. The distribution web from the harbour to the interior is well established but is likely represented by N roads not pilgrim friendly tracks