I know you're focused on 'natural' solutions - and this is not that, but I'd point you at the work of Francisco Gonzalez-Lima. He's had good results using methyl blue and near-infrared light. Both of those as he subscribes to the 'dementia as energetic crisis' model, which goes as follows: neurons and associated astrocytes (AKA astroglia) suffer mitochondrial downregulation (from causes I won't get into). This also suppresses cytochrome C production - which is critical for the remaining mitochondria (as an electron donor). Methyline blue and NIR can act as substitutes - and can possibly help reestablish mitochondrial populations. If you are able to listen to podcasts, I'd recommend the interview he had with Dr. Peter Attia (https://peterattiamd.com/franciscogonzalezlima/).
Gonzalez-Lima hasn't (AFAIK) done work with ketogenic diets and giving dementia patients alpha-ketoglutarate - but there's work out there showing positive response. This also fits that 'energetic crisis' model, BTW.
I went through similar with my mom, wish I'd known some of this before that happened. It *did* prompt me to get a readout on my genome (my mom, her brother, and their mom had late onset dementia, so APOE4 was a concern). It also got me interested in dementia, mitochondria and molecular biology more generally - but I'm a nerd. :-)