Got this question in an interview once. I just said I had taken time off for my health, and we moved on immediately.

Most people aren’t dicks. They’ll respect your privacy, because it’s unprofessional to pry. Even as an employee if you have a health issue, they aren’t obligated to know the specifics of it. You tell someone siloed off what the issue is, and they’ll communicate to everyone else that you had a serious injury and that’s it.