Being naked is not a sin, per se.
That little "per se", matters however. It means: in itself.
But since nakedness CAN BE/OFTEN IS a stumblingblock which causes lust, vain imaginations, or etc., anyone choosing to be naked in a public way is sinning, not because they aren't dressed, but because of how their lack of apparel negatively affects those who might view or even catch a glimpse.
Take a look at the common word for reproach in Hebrew sometime.
Psalm 69:20, for example, which is a prophetic insight into what the Lord was feeling and experiencing on the Cross. Also look into the Hebrew for ashamed in
Genesis 2:25.
These are the inspired words of God. They should tell you, me, and everyone who professes to believe and uphold His Word how God views nakedness.
Adam and Eve knew no shame in their nakedness because their eyes had not yet been opened by their disobedience to God when they ate the fruit.
Plus they were husband and wife, and so being naked in front of each other (since there weren't any other people in the world to see them) meant it was no big thing, either.
But once Adam, by disobedience, introduced sin into the world, and once more people, through Adam and Eve's procreation, came into the world, clothing was a given, i.e. it was expected.
So we can't use Adam and Eve's pre-fall state as some kind of litmus test to tell whether or not nakedness was inherently sinful.