Why would the clause be unenforceable? It doesn't violate any of the general principles of contract law. If you intentionally contract around these terms that don't violate any existing body of law and don't run counter to public interest, a court would have no problem enforcing the terms of a contract. They probably wouldn't sue you or me in our individual capacity if we circumvented. There's a much greater chance of recovery if they go after a company which is pretty clearly using their service in a bad faith. If ByteDance wanted to use their LLM to train their own, they could've negotiated such a license.
Sorry for the late reply, but this doesn't really seem like it'd come close to invoking any of the US's neutered antitrust enforcement. Open AI doesn't have a monopoly position to abuse, since there are other large firms offering LLMs that see reasonable amounts of usage. This clause amounts more to an effort to stop reverse engineering than stifle anyone trying to build an LLM.
I can't speak for every jurisdiction, but I'd be hard pressed to see why it wouldn't be legal in the US, especially in these circumstances. ByteDance is a massive legally sophisticated corporation, so they should've been expected to fully read and understand the terms and conditions before accepting them. They probably won't bring a legal challenge, because they know they don't have a particularly strong legal argument or a sympathetic angle to use.
They did fully not exclude it from legislation yet. Apple simply contested their iMessage's as a gatekeeper under the definition used in the act, and the Commission is in the process of determining whether or not that is true. If iMessage is determined to be a gatekeeper, Apple will only have bought themselves a few more months before they have to comply with the DMA.
If you don't mind using Meta services, you may have some luck with big discounts. I've seen BNIB Pixel 9's for as low as $475 on Facebook Marketplace, though most of them are $500-$550. I've purchased my last two Pixels through Marketplace and haven't encountered any issues.
That being said, I like my Pixel 8 Pro and the performance has been great, so I'm not sure the price difference for a brand new Pixel 9 direct from a retailer as opposed to a Pixel 8 is worth it unless you really like the squared off design of the 9.