Do you have a link to any research papers demonstrating "direct infection of brain tissues by SARS-CoV-2"? The last and most compelling evidence I saw on this was a study where about 50 cadavers from people who had recently died from aggressive COVID infections (with symptoms of anosmia) were examined, and they found no evidence of the virus infecting neurological tissues.

There is at least some evidence that spike protein may circulate in exosomes for up to four months after vaccination, although whether any of this would be likely to cross the blood-brain barrier, I don't know: https://pubmed.ncbi.nlm.nih.gov/34654691/