I forget which one, but one of the Between the buried and me albums has an instrumental release. Honestly, all of their albums I recommend regardless because the musicianship is excellent.
Scale the summit is more along the lines of prog metal but purely instrumental (I think).
Protest the hero is prog metal that has a near minimal amount of death growl (still some).
Animals as leaders which has been mentioned by several people.
Exivious is decent, I’m like 90percent sure they’re instrumental.
There’s a Japanese band called té, which is way more prog rock but you might like that.
Death, despite being one of the progenitors of death metal, is less intense on the death metal growl vocals. To me, early death metal in general is a bit different sounding than modern death metal. Regardless, Death has a pure instrumental song called Voice of the soul which is part acoustic. It’s probably one of the most acoustically beautiful songs written in the genre.
I’ve always thought sky burials are pretty cool, but as a person living in North America who has no plans to move to Tibet or take up Buddhism, that’s completely impractical. Next best thing might be for my to be placed on a body farm.