I’ve read somewhere that he never regretted building the bomb, because he believed it prevented more wars/deaths from happening. Maybe I can find the article

Edit: Found it. https://12ft.io/proxy?&q=https%3A%2F%2Fwww.derstandard.de%2Fstory%2F3000000180215%2Fzehn-fakten-ueber-j-robert-oppenheimer It’s german though. He even sued an author who wrote a play where oppenheimer was struggling with his doings