In my view it is very personal, and yes, not unchanging

"Cody Delistraty also writes:

One of the most ancient rejections of the self is the Buddhist doctrine of anatta — the belief that there is no self, or soul, or other permanent essence of who we are.

With all due respect to that esteemed journalist and The Forge, he misunderstands the Buddhist belief.

I have reviewed several definitions of “soul” in preparation for this essay and none imply unchanging personality traits. That inference is misplaced and, frankly, illogical. Buddhism teaches that there is after-life and reincarnation. Thus, Buddhism does teach that there is an eternal soul once soul is properly defined." From my https://medium.com/know-thyself-heal-thyself/eternal-soul-properly-defined-fe7a93e534f8