Not a 'new proof' - it's never been proved. Also, from a quick google, Atiyah is 89 and has made a couple of other very dodgy claims in the last couple of years. He's more 'a giant' than just 'respected':
He recently claimed a very very dodgy proof of non-existence of complex structures on the 6 sphere. I think it's well known in the community that he is not mentally stable, which is very sad as he is a very accomplished man.
From online chat, I'm not remotely qualified to judge that.
https://en.wikipedia.org/wiki/Michael_Atiyah