The interesting bits from the text[1], relative to the now flagged sibling
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(3) FOREIGN ADVERSARY CONTROLLED APPLICATION.—The term “foreign adversary controlled application” means a website, desktop application, mobile application, or augmented or immersive technology application that is operated, directly or indirectly (including through a parent company, subsidiary, or affiliate), by—
(A) any of—
(i) ByteDance, Ltd.;
(ii) TikTok;
(iii) a subsidiary of or a successor to an entity identified in clause (i) or (ii) that is controlled by a foreign adversary; or
(iv) an entity owned or controlled, directly or indirectly, by an entity identified in clause (i), (ii), or (iii); or
(B) a covered company that—
(i) is controlled by a foreign adversary; and
(ii) that is determined by the President to present a significant threat to the national security of the United States following the issuance of—
(I) a public notice proposing such determination; and
(II) a public report to Congress, submitted not less than 30 days before such determination, describing the specific national security concern involved and containing a classified annex and a description of what assets would need to be divested to execute a qualified divestiture.
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The way I read this is that Congress is bootstrapping the law with its own finding that ByteDance, Ltd/TikTok are Foreign Adversary Controlled Applications, but then, in (3)(B), the President is responsible for determining any other entities this law should cover given previously stated parameters (what they mean by "covered entity" here), using the procedure it then provides.
I believe that addresses the concern about this being a "Bill of Attainder".
Edit: Obviously IANAL, but it also doesn't appear that this issue of this being a Bill of Attainder was raised by TikTok, nor was it considered in this opinion. Perhaps they will do so in a separate action, or already have and it just hasn't made its way to the court(?), but if it were such a slam dunk defense, you think their expensive lawyers would have raised it.
[1]: https://www.congress.gov/bill/118th-congress/house-bill/7521...