It's not unusual for the details of a Kickstarter or Indiegogo campaign to change between the funding and fulfillment phases. In most cases, the changes are minor, not affecting the usability or deliverability of the product. In the case of Shenmue 3, the change is enough to require refunds to backers.
During the funding phase of the campaign, the company promised that backers would receive a Steam key on the day of the game's launch. That promise was logical at the time, as Steam was really the only game in town. In the three years since the campaign ran, things have changed. Epic Games and Discord have both launched their own game stores, with Epic taking the approach of signing exclusivities.
Unfortunately for backers of the Shenmue 3, developers YSNET and publisher Deep Silver made a deal with Epic for a year of exclusivity on the Epic Games Store. This means that it is not possible for them to accurately fulfill their obligation, as there will be no Steam access to the game at launch. Epic Games CEO Tim Sweeney claims that the fault lies with Valve, who will not allow them to generate Steam download keys a year before the game will be available for purchase, though this is an insane claim. The fault lies with the publisher who has chosen to change the promised distribution method at the last moment. Plus, giving backers a key that they cannot use for at least a year would not have been a better situation than not fulfilling the obligation at all.
Because of this exclusivity deal, backers who are not interested in participating in the Epic Games Store ecosystem can request a refund from the company. The refunds will be paid out by Epic Games, as part of the deal. If backers are still interested in receiving their fulfillment via Steam, the keys will be sent out one year after Epic Games Store launch, but you must specifically request this option.