i struggled with concentration issues, too, after my 4th infection for a few weeks. What i didn't do the last time is to take ACC/NAC (Acetylcysteine) against the cough and slime during the ongoing infection. Its just an expectorant (? I googled the translation. Does this word even exist??).

So, just in a reason of prophylaxis and getting rid of the last coughing, i took acc/nac for a week and I felt an relieve with my concentration issues. Then, just because I'm interested in human body & illness & medicine in general, i saw a few (german) studies that concluded, that ACC/NAC does somehow help with post-covid symptoms.

here is a start for this topic:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7649937/

its an early study, but its just for the start :)

wish you a fast getting-better!