Information warfare is a domain of war in the 21st century.

The Scotus case linked to here by others has noted the possibility of tying networks of contacts to Tiktok user profiles, and network mapping political groups in Taiwan can be leveraged to support any number ventures to disempower the island's democracy-favoring majority.

does the US ban apply to taiwanese people in taiwan?

Only insofar as their support networks extend into the United States. But you're right to suggest that Taiwan should consider a ban also, over similar security concerns.