If these changes are not hurting user metrics are they really making their lives miserable? When you are optimizing an experience for billions of users, numbers are the only thing you can trust.
I suspect there is no metric specifically answering the question "do users want [enshittification of the day]?"
There are probably plenty that measure success with dark patterns however, like viewership and engagement.
Classic example: reactions and watch time as measuring engagement. Leads to shittier content being promoted because the more garbage something is, the more outraged people will be.
And that's why Facebook has "optimized" itself to be as shitty of a platform as humanly possible.