Having unlimited PTO and coping with absences at work are orthogonal problems.
When you are going on vacation you can pick somebody in your team as the to-go person and communicate that fact to them, to your manager, and add that information to your automated "out of the office" emails.
When you are going on vacation you can pick somebody in your team as the to-go person and communicate that fact to them, to your manager, and add that information to your automated "out of the office" emails.