How do fractional shares work

Sorry if this is a stupid question but i have been curious for a while and ai didn’t give explanation that make sense to me . How do brokers and exchanges provide the service of buying and selling fractional shares? There are several models in my mind, when an investor states that they want to buy 0.5 of NVDA shares the broker then absorbs the other half. Another solution that i can think of is that the broker simply creates some sort of token that follows the stock’s current price when they buy and sell. Those two solutions leads to the same problem that is the service provider would have to bear the risk of those stocks for them which doesnt make sense. Please enlighten me sorry if this is not the right sub to post this. Thanks in advance