Hypothalamus not really involved in memory formation, in my understanding. Most people clear the virus within 2 to 4 weeks of infection. There is no live virus found in autopsies of brains of those infected. Anosmia cause probably more peripheral not brain infection.

Brain fog likely caused by persistent immune disregulation, likely including some mechanisms Patterson has proposed, and others.

There are lingering cognitive deficits in other post viral or acute bacterial infectious syndromes which don't involve anosmia.