Congress can more or less do what it wants for things like this (under the guise of "interstate commerce"). They can write up a bill that says "TikTok is banned", and if it's passed and signed... that's that.
Certainly the Biden administration can't ban it on their own unless they can figure out how to use existing regulatory power in a way that the courts will uphold.
Congress can pass whatever they like, but there's a bunch of reasons a law like that would be unconstitutional and likely quickly struck down. Not only is it a violation of the First Amendment, it is almost a textbook case of a Bill of Attainder.
(At least, to to my layman's understanding. IANAL.)
Certainly the Biden administration can't ban it on their own unless they can figure out how to use existing regulatory power in a way that the courts will uphold.