I haven't come across any reviews that I could recognize as having been blatantly LLM-generated.

However, almost every peer review I was a part of, pre- and post-LLM, had one reviewer who provided a questionable review. Sometimes I'd wonder if they'd even read the submission, and sometimes, there were borderline unethical practices like trying to farm citations through my submission. Luckily, at least one other diligent reviewer would provide a counterweight.

Safe to say that I don't find it surprising, and hearing / reading others' experiences tells me it's yet another symptom of a barely functioning mechanism that is peer review today.

Sadly, it's the best mechanism that institutions are willing to support.