In theory none? Stock buybacks increase the stock price but reduce the number of shares. So the market cap should stay more or less the same.
It reduces the number of shares on the public market, not the total number of shares.
This can drive the price up if there is high public demand for the now reduced number of shares available
$110B in stock buybacks to raise the market cap by some $300B seems like a good deal —— or the market is pricing in new information that was announced much more recently than the buybacks
It's just AI hype from the keynote.
I’d say there is also the facet that Apple’s AI has strong privacy guarantees, and Apple has a good track record with privacy
Pretty much every other offering is a privacy nightmare, including MS and their recall and many folk don’t want anything to do with AI as a result