Is it actually a free speech issue, though?
It's not as though SCOTUS is trying to rule on whether to ban short-form video or content from particular person. The allegation in regard to TikTok isn't 'dangerous speech', it's the platform's collection of user data and the manipulation of available content via an algorithm that they claim is a tool of a hostile foreign entity. Neither of those issues constitute 'speech' whether related to a foreign or domestic company.
It seems to me like this is being framed as a speech issue to protect other vendors with hostile algorithms. If Google were forced to stop pushing AI and paid results to the stop of its searches, would that be a free speech issue? If Facebook were forced to put more weight on users' choices about what shows up on their feed rather than pushing dodgy political posts and paid advertisements, would that be a speech issue?
Honestly, deciding that toxic algorithms are protected speech seems like a much more dangerous precedent to me than coming to a conclusion that a company that's beholden to a foreign entity that may be forcing it to engage in hostile intelligence operations and soft power can be restricted.
If someone made a piece of malware that ropes your PC into a botnet and uses it to perform DDOS attacks, would banning it be a speech issue if it happens to come in the form of a blogging platform? A chat client? A music sharing service?
Just having speech on a platform doesn't mean everything that platform does qualifies as speech and requires first amendment protections.