Only a small fraction of PhD graduates in STEM end up as (tenured) professors. For example, see this question and plenty of other material on the internet.
Many PhD graduates end up wokring in government or industry. Some of those are research positions where a PhD is valued if not required (perhaps the specialisation is less important), but I also know STEM PhD graduates who work as programmers (quite common), as a miner, in the military, or as a reindeer herder (yes).
Within STEM, what fraction of PhD graduates end up in jobs for which a PhD is a requirement? And what fraction in jobs for which it is considered valuable, even if not required?
In order not to muddy the waters with graduates doing postdocs still hoping for an academic career before giving up, let's consider the first long-term (5 years+) position or whatever they're doing 10 years after completing the PhD.