#2 He is already getting booed

It shouldn't really be that complicated. Goldberg defeated one of the WWE's greatest modern-day creations to win the Universal Championship much to the chagrin of the fans. The reaction to him on SmackDown suggested that Goldberg's road to WrestleMania will be pretty bumpy.
The Hall of Famer soaked in the boos and laughed them off, so maybe he will continue to embrace the heat and become a full-fledged villain. There have been so many times when a WWE had been forced to turn a Superstar heel after a negative crowd reaction, with this probably being one of them.
The company should just go all-in and make Goldberg a bad guy, to go with the flow. It isn't even necessary for him to remain a babyface, unlike when he was getting booed during his first Universal Title reign.
Turning Goldberg heel would enhance his run and fit the narrative perfectly, as he won the belt from the hottest full-time star in the company. The heat is perfect for the story.
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