US Federal Law does NOT require that bills only deal with a single issue. So, a single bill could send aid to Ukraine, outlaw hats and declare Tuesday, “puppy kicking day”. And that would be fully within the US Constitutional method for passing Federal laws. All that matters is that the exact same text is passed in both The House of Representatives and The Senate and is then signed by The President. There’s a whole bunch of other stuff around it (veto process, and filibuster), but the ELI5 version is both houses of Congress pass the same bill and the President signs it and thus it becomes US Federal Law.

There will, of course, be a whole other process around the law being challenged in the Courts. ByteDance will undoubtedly challenge the TikTok ban in Court. And that will take years to fully wind it’s way through the system. And the courts may issue an injunction, preventing the law from being enforced, until the decision is made. Basically saying, “nope Federal Government, you cannot enforce this until we say so”. Personally, I would expect that in this case. So, don’t expect TikTok to leave the US any time soon. Note that, this can be done to part of a law (again, I would expect this) and not the whole law at once. So, this won’t imperil US aid to Ukraine, Israel or Taiwan. It just means that we’re likely to see the bounds of US Federal Government power tested a bit. Does the US Federal Government have the power to unilaterally kick a company out of the US? I’d bet on “yes”, especially with the ties to national security. But, I could easily lose that bet.