He doesn't go into it but JMH mentions dead lifts and much else as being crucial to preventing SN. https://www.jamesmarkhayden.uk/stories/shermers-neck-and-how-i-dealt-with-it
Actually what he says (my bold) in the linked article is
“You
don’t need to be doing bicep curls, butt planks, deadlifts, hollow body holds or kettlebell movements“
I suffered Shermer’s Neck on WAWA 2016 at 1850km, eventually retiring at just over 2,000km and just over 100km left as I could not ride safely, with a lack of forward vision. I wasn’t the only one on WAWA struggling with Shermer’s but I was the only one it came on early enough and deteriorated enough that I had to stop. About 10% of the field were affected.
Body weight exercises
Neck stretches
Swimming
General all over strength conditioning have helped me. IMO. Bear in mind my longest ride since 2016 is 1,000km where even before conditioning I never had issues. But I would say you do not need to do anything beyond body weight stuff for resilience.
There’s also changes I made on the road bike to ensure my neck was better aligned with the body when riding to reduce the stress it’s under. The faster you can ride and more time off the bike the better obviously in terms if Shermer’s.
But I’m trying to go recumbent full time for long distance now having jumped between recumbent and road bikes over the past three years. My recumbent eliminates the neck and other discomfort issues entirely.