Me too, brain fog is me. I can usually comprehend...but not remember. If it involves correlating lots of facts, then I cannot do it. Literally, like a computer, I run out of memory.
I used to have a photographic memory...about
the time I started having bouts of "appendicitis" and other gut problems, the film ran out. Now it is one of the major reasons I don't work. Trying to remember even "obvious" recent facts is like staring into a coal cellar at midnight.
Declarative memory (names, dates), prioperceptive memory (where I just put something) short term memory (what I was doing five seconds ago - often even how I started a sentence, when speaking to people, what I intended saying) and just plain recognition. All shot, I can count on the fingers of one hand the numbers of days each year that my brain is working anywhere near normally. On meds I always find cognition is the first thing to go; winter is so much worse than summer, I'm beginning to think Vitamin D is something to do with it.
Try learning to drive when you don't remember what gear you are in or where the different gear positions are....
Guess which emoticon represents me, guess which one is the driving instructor !