EyeBreak

EyeBreak sits in the menu bar and, every 20 minutes by default, dims the screen with a 20-second countdown to look at something about 20 feet away. You can snooze or skip any break, and the menu bar can show the time to the next one. Breaks are held while another app is full screen or the screen is mirrored. Optional blink, warm-compress and artificial-tears reminders are available, and habit stats are kept on your Mac. It is for people who spend long stretches at a screen and want a gentle reminder. The README says it supports comfort and does not claim to improve vision or diagnose anything.

It needs macOS 13 or later, and the README says it requests no permissions and makes no network calls. The download is ad-hoc signed and not notarized, so the first launch has to be allowed in System Settings under Privacy & Security. On notched MacBooks, the menu bar icon can land under the notch in a crowded menu bar; the README explains how to move it.