Hmmm. Tough question. I don't know any retired bankers, apart from your good self so I have no point of reference but I do know some retired solicitors.. Depends on the term "banker". If you ere one of these hedge fund rich as Croesus types a la Rishi Sunak or that American who worked for Barclays and owns race horses Richie Rich(?) then probably super scruffy. A less rich, more mainstream banker probably would dress down to T shirts, maybe a hoodie , tailored shorts in the summer.
By the way - you can really tell from those two pics that you have lost weight.