Entirely anecdotal but I did notice a marked shift towards even more erratic behaviour and dissonant, often contradictory utterances after his second disclosed Covid bout back in March this year and since then.
IANAD, not a medical opinion, etc., etc., but I wouldn't be surprised if a dementia diagnosis is in his near-term future.
I've wondered this too.
I've never been a fan of Elon but watching him burn what took a lifetime to build (whether deserved or not) is fascinating and shocking.