That's really interesting, I personally don't read those tone differences based on the casing. Neither approach carries different warmth or formality to me at all.
I wonder if this is a regional or generational thing?
It's definitely primarily generational. In my experience, capitalization-as-tone is used by many Generation Z people. On the other hand, it is not widely used by older generations, or the younger Generation Alpha.
Generational is a good bet:
https://news.ycombinator.com/item?id=41537994