I've read online that "Bacopa Monnieri" is a particularly strong and researched herbal supplement for cognitive maintenance, enhancement and neuroprotection, with the potential of supporting neurogenesis.
I've not tried that stuff since money is hard to come by these days. There have been a few human studies.
You can find more info here:
https://pubmed.ncbi.nlm.nih.gov/?term=bacopa+monnieri+cognit...
and here: