If your org has engineers LLM dumping into your MRs/PRs, make it policy that code reviews require a live-review session where the engineer who wrote the code walks the other engineers through the code. This will rapidly fix your problem as the 'author' of the code who cannot explain his/her code will not want to be grilled this way ever again.

Accountability is the real answer. If you don't enable individual and team accountability, then you are part of the problem.