Doesn't clean room typically apply to cases where the "dirty" team has legitimate access to copyrighted code, like the IBM PC BIOS which was published in the technical reference manual, and uses this access to write a functional specification for the "clean" team?

I'm not sure how clean room would apply to commercial applications distributed in binary form, as there's no way to look at even disassembled code without violating the license agreement and therefore being in breach of contract and subject to potential copyright infringement claims for copying or even continuing to use the software, let alone cloning it, and surely you're not going to be subject to a copyright claim based on familiarity with the application from merely using it.

The issue is that LLMs very likely have access to the source code of these products as part of their training data, and are then being used to generate clones. There's no barrier in the middle to ensure copyright violations don't leak

The reason why 'reverse engineering' has gotten so good is because what we're actually seeing is fully automated luxury plagiarism

The practical uses are more applicable to laundering open source code covered by copyleft licensing like GNU.