Celebrity endorsement has never been a factor in how well a videogame does either way, regardless of level of star power or degree of involvement for the celebrity: Keanu Reeves playing a heavy hand (heh) in the story of Cyberpunk 2077 did little to stop the game's initial bad press, and the main reason Baldur's Gate 3 did well isn't because JK Simmons is playing Kethric Thorm. (still, he had a great performance). Gameplay matters a lot more for a videogame.
It's unsurprising then, that Oscar winning actor Will Smith's involvement in a game in the oversaturated genre of zombie survival shooters did not become successful.
Plus, I don't think paying celebrities to promote videos on their YouTube channel is an effective marketing strategy, mainly because nobody really watches any celebrities' own YouTube channel, with the exception of Jack Black's gaming channel, of course.