On trail, try this
https://youtu.be/7nqy3zvR65c?si=Rogub2uFfNxBkWv7 (one simple exercise).
The idea is you look at your feet all day to avoid tripping on rocks or stepping on snakes. This is something you can do quickly every morning and every evening to balance that out.
At home, try these:
https://www.surreyphysio.co.uk/top-5/best-5-exercises-for-cervical-kyphosis/
On trail, you can use a subset:
Neck rotation overstretch
Rotate your neck to its end of range. Place the palm of your hand on the side of your head, and gently push your neck into slightly more rotation. Hold the stretch for 15 seconds, and relax. Repeat three times. This is an excellent exercise to improve rotation and mobility in your neck.
And
Stand or sit up tall. Focus on an object at eye level while slowly moving your head back over your shoulders and tuck your chin in. Gently guide the movement with your hand on your chin. Hold for 3 seconds then relax and return to the initial position. Repeat 5-10 times, 3 times per day.
https://www.lifemark.ca/blog-post/banish-neck-hump-exercises-improve-pain-and-posture
Some good stretches
https://happytrailsandwanderlust.wordpress.com/2017/11/07/suggested-trail-stretches/
I have to admit that in the evenings on trail I’m too tired and in the mornings we are ready cut out any delays. But stretches can really be good.