It isn't the push-button setup that you've built, but PiHole is a decent option for this purpose as well.

Occasionally I add social media sites (including HN) to the block list.

It's very easy to bypass when I really want/need to, but it does cut down the more unconscious "CMD + T - news/redd/face - enter" moments that happen when I'm bored.

Prevents the occasional unnecessary mindless scroll by creating a couple extra steps.

That's exactly right - It's always good to put roadblocks and increase resistance to bad habits, and take away roadblocks and decrease resistance to good habits. It works better for me than cold turkey.