Romans 2:12 For as many as have sinned without law will also perish without law, and as many as have sinned in the law will be judged by the law 13 (for not the hearers of the law are just in the sight of God, but the doers of the law will be justified; 14 for when Gentiles, who do not have the law, by nature do the things in the law, these, although not having the law, are a law to themselves, 15 who show the work of the law written in their hearts, their conscience also bearing witness, and between themselves their thoughts accusing or else excusing them) 16 in the day when God will judge the secrets of men by Jesus Christ, according to my gospel.
Romans 1:20 For since the creation of the world His invisible attributes, His eternal power and divine nature, have been clearly seen, being understood through what has been made, so that they are without excuse.
God is talking about SINNERS, who, not having heard of Him, do evil towards their fellow men,or deny there is a God.
Many American Indians who never directly heard of God worshipped the "Great Spirit" & acted honorably toward their fellows. Just as Scripture says, they knew instinctively there's a Supreme being who's a Spirit. While many believed that animals had spirits as well, they knew there's only one Supreme Being. Same for many isolated peoples on other continents. They instinctively knew what was right & honorable, not to commit adultery, etc. Naturally, there were evildoers among those peoples who planned war & pillage against other people, & who denied there's a God.
But JESUS knows who's who among those people, & I believe He saved those who did right without having never heard of God or His law.