Roblox RBLX posted a relatively weak end to 2021, with slowing user growth and engagement in the U.S. stoking fears that the firm won’t be able to continue its momentum coming out of the pandemic.

Roblox is one of the most popular games in the world right now, regularly topping the most-played charts on PlayStation and Xbox, with over 380 million monthly active Roblox users across all platforms ...