The FTC would enforce the rules, treating violations as unfair trade practices, while state attorneys general would have the power to sue companies and protect their residents.
Large game publishers like Activision Blizzard, EA and others have typically objected to regulation like this in the past, in some cases even defying local laws until they had no choice but to comply. They have made concessions, such as disclosing the general contents of loot boxes and shifting any in-game transactions to cosmetics. The efforts have occasionally required rebalancing whole games to make progression fairer for those who aren't willing to pay extra.
There's no guarantee the Act and its necessary House of Representatives equivalent will pass, or that the President will sign it it into law. If the bill clears those hurdles, though, it could have a profound effect on game development. The measure wouldn't necessarily hurt Fortnite, Apex Legends and other titles where purchases are usually for cosmetics and made on a per-item basis. It would, however, prevent companies from tricking you into paying more than you wanted just to enjoy yourself.