As far as I know:

A romance scam.is a fraudster who take someone else identity to trick other person online and lure them to give the scammer money. They tell they love their victims and ask for money and they just want money from the victim rather than love. The scammer and victim never if ever meet each other. They can be very hard to spot without paying attention to key red flags and they can leave their victims financially broken.

A gold digger on the other hand has a serious relationship with the other one and they meet each other in person but rather than love the gold digger only engage with a wealthier person because of their cash and wealthy rather than love and companionship. Mostly women do this. Male gold diggers are rare.

A sugar daddy/momma seem to be the most honest relationship of the three. A much older person engages with a younger one in a true relationship meeting and physically interacting with each other. However its a kind of contract which they meet each other and they can have sex or not with the objective of the sugar daddy give money and other resources to their sugar babies.