They’re probably going to find themselves having to explain what it means that a social media platform is itself engaged in speech, instead of functioning as a platform for others to speak. TikTok users, whose voices are allegedly curtailed by the ban, aren’t exactly prevented from going to another platform.
If they say that it’s Tiktok’s speech that’s curtailed, they’re going to have to explain carefully how they’re not a foreign influence operation.
The language of the first amendment is pretty stark, but the courts have always understood it has various limits.