The incumbent in this space is https://www.beeminder.com where the specific use case shown here about screen time can be configured with e.g. their RescueTime integration. Beeminder however just take your money for themselves as opposed to giving it to charity. They claim people would otherwise be more prone to giving up on their goals, thinking "oh well, the money is going to charity anyway so I'm doing a good thing by breaking my commitment". The opposite approach would be setting it up so the money goes to an organization whose goals you disagree with.