This seems like a screening problem and a checkpoint problem. Immediately, I’d just cut them loose and hire a new dev to recreate the work. Screen the new one

This seems like a screening problem and a checkpoint problem. Immediately, I’d just cut them loose and hire a new dev to recreate the work. Screen the new one better and have lots of checkpoints. By screening, maybe adjust your interview process to cover previous work and culture fit. Check references. For checkpoints, set up daily check-ins for code with an automated build and test that checks that it at least compiles and does something. And check-in with communication to talk with them as much as you can to include them in design and requirements decisions to share context and get their input.