[souffle]

Hi there - that's a beautiful hamster for sure.
I would say this is a male hamster. There is a large gap between the two vents typical of a male and the scent gland is more obvious.
You hammy looks closest to a Normal pearl winter white though it is possible he might be a marbled WW colour or possibly a Normal that is partially in winter coat. If he changes back to fully brownish as the weather warms you will know he was in winter coat.
Sometimes when they sit very still on their tummy and go flat they are a little bit unsure so they make themselves low and flat and don't move. They may wander around if you cover them over with your hand but as he grows in confidence he will likely stop doing this.