Metacognitive clutter is stuff that makes higher mental states not work well.
An individual example might be holding a mistaken view of your role in some organization or activity. Your mistaken view causes much of what you are doing to be wrong and to detrimentally entangle other parts of your life.
A national or social example of metacognitive clutter might be the many dumb subjects and shallow statements required of American politicians. See the following for a more detailed analysis: Semiotics in politics and the totalitarianism of PC.
Another area where metacognitive clutter causes a lot of problems is interpersonal relations. If you cannot speak to your SO and/or closest friends from a metacognitive point of view, you sort of don’t really have an SO or close friends.
In this context, metacognition means being able to talk about how you understand each other and why you think, feel, and behave as you do.
Good interpersonal metacognitive communication produces better relationships, happier people, and healthier individual psychologies.
This happens because good communication removes metacognitive clutter, greatly reducing interpersonal mistakes and cognitive entanglements.
I, for one, do not believe you can do really good metacognitive communication without a prior agreement to do that and a technique that reliably works on small details. See this for information on such a technique: How to do FIML.
General discussions on beliefs, biographies, emotions, philosophies, religion, science, and so forth are helpful, even essential, for good metacognitive communication but they cannot by themselves remove the idiosyncratic clutter that has built up in the mind over many years.
Meso and macro level techniques cannot remove micro clutter, especially idiosyncratic micro clutter which we all have a lot of.