Hey! :)
I had the pleasure to have two meetings with Aurora Borealis so far, hopefully I will experience that magic again. To answer your question, I always use manual focus on my widest lens, 16-35mm f/2.8.
I set it to infinity minus one, as we call it here, that's the small line just before the infinity sign on the lens focus ring.
Another parameter I fix is the ISO, values between 800 and 1600 are the best as this way the sensor captures more stars, more details in the night sky in general. Depending on the intensity of The Lights, the exposure times I try is within the 2 - 20 seconds, at least that's what was working the best for me back then.

I hope that helps! :)

Ah, also in post-processing I don't use noise suppression as it also kills the details in the sky.