Is It Possible Photo & Video Files On iPhone To Reappear After a Factory Reset?

Hello Mr. Gary, I want to ask you a question. How to reset iphone permanently. On my iphone there are files that are “private” and I have moved them to the hard disk. I’ve known on Android, that even if the phone has been deleted and reset, there is still something that can bring back the files that were there. Is this possible on iphone or macbook? I am afraid if the file is spread online by irresponsible people. Because I have plans to sell my iphone and macbook. Thank you for your help and time Mr. Gary.
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Archie