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SurveyJS
Open-Source JSON Form Builder to Create Dynamic Forms Right in Your App. With SurveyJS form UI libraries, you can build and style forms in a fully-integrated drag & drop form builder, render them in your JS app, and store form submission data in any backend, inc. PHP, ASP.NET Core, and Node.js.
Interesting concept, might try it! I've used Quitter (https://marco.org/apps) for months to auto-quit my email app & Slack after a time interval. This is a more proactive approach.
You'd still have the issue of being able to open multiple browser tabs, and they can be more distracting than apps. But there are already plenty of browser extensions for that; personal fav: the Defaulter in https://github.com/louisbarclay/nudge (unfortunately temporarily unmaintained)