Cognitive exertion is uneven?

Does anyone else have a really uneven pattern of cognitive impairment/PEM?

When I have enough capacity I can still think very deeply and critically. I can do things like writing, editing, research, and other "deep work" and I can feel intellectually like myself.

However executive function type work absolutely destroys me--multitasking, switching between tasks, prioritizing, interruptions. Technically, this executive function type work should be "easier" but its basically impossible for me. It brings on brain fog, and uses up my cognitive capacity very quickly. I also lose access to deep thinking, I can't write, research. think clearly, retrieve things properly and if I keep pushing I crash.

If I was able to spend that same capacity doing deep work, I would be able to function for much longer.

I have ADHD but it was diagnosed after I got sick and I have benefited from ADHD meds but they just exacerbate this issue--I can focus very well but I get even worse at multitasking, ironically and still crash.

I'm just trying to figure out if anyone else has this where cognitive difficulty isnt necessarily proportional to how demanding something is.