I would review it and immediately tell them to break it into bite sized PRs.
My coworker kept doing that. We had several talks about it. Other members of our team had talks about it with them, and even our manager. Finally, I marked the PR as needs work, told them to break it into several PRs. They weren’t happy, but I was tired of dealing with PRs that were 30+ files, unrelated in change, and over 1500 lines of code changes. They were pretty mad at me for a while. But it stopped shortly afterwards.
It shouldn’t take more than an hour to review a PR.