Sforno on Exodus 33:20/ספורנו על שמות ל״ג:כ׳

1ויאמר לא תוכל לראות, your inability to see what you would like to see is not due to My depriving you, personally, of such an experience, but is rooted in man’s inability to “see” such things unless you had died first, as an eye of flesh and blood cannot “see” such things. You would be fatally blinded before understanding anything you would “see.”