It's not a "claim", Lee, it's a proven fact that they can influence emotions, which are known to influence behaviour:
https://www.theguardian.com/technology/2014/jun/29/facebook-users-emotions-news-feeds
"Some of the clearest examples of criti-hype today center on the role of social media in our lives, especially the claim that its designers can directly and effectively influence our behavior."
#LeeVinsel, 2021
https://scribe.rip/youre-doing-it-wrong-notes-on-criticism-and-technology-hype-18b08b4307e5