Safety of Clearing Memory of iPhone

Hi all! Just have another question. Considering the option to return / replace my iPhone 11 Pro while under warranty.

My Question: if I delete all pictures and related data from my iPhone, will the next user still have a chance to retrieve my deleted pictures or data? I heard not sure tho if true, there are apps or the like that can still retrieve deleted data or pics from the iPhone. Because I saw somewhere the that all files, data or pics are still locatable and can still be retrieved in the iPhone unit.

So just wanted to get your thoughts on this. Thanks in advance for your time to look and reply.

are the pictures saved in my iPhone