He would have had standing had he sued in Georgia state court. Standing in federal court is much narrower.
There is something in federal court called the "general grievance" doctrine, which says, basically, that if everyone has standing, no one does. The idea-- and conservative judges created this doctrine, to limit judicial activism-- is that if everyone is equally affected by a rule or decision, then they can overturn it through their elected representatives; only if something affects someone in particular, in a way that others are not affected, do they have standing to ask a federal court to overturn it. Therefore, in a post-election dispute, the defeated candidate has standing, but the average voter does not.
Standing in federal court is much narrower.
Unless Judge Sullivan is presiding.
Is the 11th an appeals court?
So if Trumps lawyers appeals there then he has standing!