If you want an app can force you take a break, here it is.

You can make your computer remind you to practice good work ergonomics and break habits with Take a break app.

Take a break allows you to customize how often breaks happen, how long they are, and more. It reminds you not to tense up or sit in a poor position.

Take a break allows customization of audio alerts and other essential settings. If you want simple you can't get much more basic (yet effective) than this.

With the app you can set and let it force you to take a break, there's no easy way to leave the break screen. If you don't like this, just uncheck Show floatting window for break.