He's kinda boring to me

I like Redford's work, but I see where you're coming from. He didn't have a distinctive personality as many of the peers of his generation (Nicholson, Newman, Eastwood, etc). Sometimes this laid back aspect of Redford fits his characters very well (Butch Cassidy and the Sundance Kid, Jeremiah Johnson, The Natural). I also think there are a few exceptions where he shows a greater range. The films that come to mind are Three Days of the Condor and The Sting. Probably above all else, Redford has benefited immensely from his choice of films. At least 5 of his films are among the best hundred or so movies from 1969-1985, and rarely was he in any total stinkers (unlike Paul Newman, say).

Redford's weight and presence as an actor mirrors a lot of previous actors who could be called stoic or boring. Gary Cooper, Joseph Cotton, and George Peppard come to mine.

I've never been too fussed by him (or his movies) but have been slowly watching his back catalogue during lockdown and (to be fair) he's made some fair (always serviceable) interesting movies.

But (alongside Warren Beatty) he has zero personality (outside of semi-adequate line recital) Other than his looks, he never seems committed as an actor. It's as if he's on autopilot throughout (incapable of genuine emotion, regardless of the role) his 'performance-dial' turns up no further than mediocre.
Yet he has an interesting 'presence', because you always expect a tonal shift (that he seems either incapable of, or disinterested in giving?) It's an acting-straightjacket of his own making (sadly)

There seems to be another 'theme' I've noticed in his mid-to-late output, that dictates he's always the calm, collected, nobel, go-to-guy, invariably in charge and usually pitted against corruption or dishonesty. Irregardless of the threat and/or problem, he stoically walks through either (plus his surrounding cast) with an (almost) vague disinterest.

Which is a shame, because there's always the threat of substance (to match his matinee idol demeanour) lingering underneath all his movies!

He is a bit stiff, but it has usually worked for the roles he has had.