If AI generated code is not copyrightable, releasing it under an open source license is meaningless.

Under those conditions it would be un-licensable (since a license is essentially an agreement not to sue for copyright infringement) but it can still be made open by publication. I'm skeptical that the "anything that comes out of AI can't be copyrighted" argument will end up holding, but in the meantime it provides a strong incentive not to make that code public.

Releasing it for sure is meaningful

I'm not sure you understand all the things that an OSS license does. For example: liability.