Francisco Gonzalez-Lima has done some interesting work with AD patients in which the issue appears to be downregulation of cytochrome c oxidase, a key electron donor in the electron transport chain that is critical to mitochondrial function.

He's had success using methylene blue as a 'substitute' electron donor as well as near-IR light through the forehead (photons act as replacement electrons - won't get into the physics, but photons aren't super different from electrons) in the frontal lobes (area right behind the forehead).

From the descriptions of 'brain fog', it seems there's a major 'executive function' component - and the brain area associated with executive function is the frontal cortex.

So... I have to wonder if anyone has tried IR light to the forehead as a potential therapy(?)

If you look at Gonzalez-Lima's work on PubMed, you'll see he was using 1005nm light to sidestep absorption by hemoglobin - and the cranium appears to transmit this light.

Just a potential hypothesis...