Don't give up on your little hammy! Sometimes different hamster's take longer to tame than others! I would keep doing what you are doing, putting your hand flat out and putting the treats in your palm. You could keep trying to keep give him treats until he is
super comfortable with that before moving to the next step! The most important thing during the taming process is to have patience! After he finally can take the treat off of your hand without being scared you could try taking him to the bathtub, but only once he is comfortable, remember patience is key! You could also try to take some tissue/toilet paper and rub it against your hands to rub your scent onto them, then place the tissue/toilet paper into the cage. This is an automatic way for your hamster to get used to your scent because they will probably use it for their nest and sleep with your scent all day long
! Also, you can try talking to your hamster softly through the cage just so he can get used to your voice. Taming just takes time
Another way to greet your hamster too is to use the back of your hand and gently place it in front of their nose so they can smell your scent and become familiar with your hands.
Good luck!! I wish you the best