This article is somewhat misleading.
The court only ruled that "OpenAI" is descriptive. It did not rule that it can never be registered.
A descriptive trademark can still be registered with evidence that the mark has become distinctive through use -- that is, that "OpenAI" is known to the general public to refer to their company, rather than simply describing a type of AI.
It appears OpenAI have already made that submission separately:
The Board of Appeal also stated that, once the contested decision has become final, the proceedings will resume for the purposes of examining the applicant’s alternative claim based on Article 7(3) of Regulation 2017/1001, relating to distinctive character acquired through use.