Lookaway
Every 20 minutes, the screen takes over.
Look about 20 feet away for 20 seconds. Notifications were too easy to swipe away. This actually takes the screen.
Free. Unsigned: Mac → Privacy & Security → Open Anyway. Windows → More info → Run anyway.
This is the Small Eye icon that counts down the timer.

This is the menu.

This is the Overlay you will see.

I built this because I sit on a laptop all day and my eyes get fried. The 20-20-20 rule is what the American Optometric Association and the American Academy of Ophthalmology recommend for digital eye strain. It eases symptoms. It is not a cure.