Though the title says chronic fatigue the article is about chronic fatigue syndrome https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-020-02666-5
There have been a few groups who have used a broad-based look for infections, not just specific human viruses, but using pan-viral microarrays like the Virochip which can detect fragments of viruses belonging to other families (it should in principle detect zoonotic viruses). I would have expected such studies to note if there were unusual findings with respect to Anelloviridae or Circoviridae. The author doesn't talk about specific mechanisms about how these viruses could induce the illness beyond a general mention of crossing the blood-brain barrier and causing tissue damage.
This theory could explain why many people seem to get permanently worse after a crash. Namely blood barrier gets compromised temporarily (stress, another virus, etc.), this allows more virus to enter the brain, then viral load in the brain increases and settles down to a higher level than before the crash. This higher viral load then leads to new and / or more severe symptoms than before.
interesting that the author is from the Norwegian Institute of Public Health. Never heard of him before, but he has a Wikipedia page. https://en.wikipedia.org/wiki/Bjørn_Grinde