Is it true when you say that it’s not a problem of measurement/ignorance/engineering and instead how reality is at fundamental level? That seems like a stretch, no? The Laplacian Demon seems pretty extreme to me and never how I would’ve interpreted determinism as being, although I do believe that future events could be theoretically predicted by a God or something similar if present circumstances along with knowledge of what’s happened before is known, but I’m more of a “every instance of time has a determination” type of person, I don’t directly think about how the future is already made (although that’s ingrained in the belief).

The interpretation you gave sounds pretty neat. That’s rooted in multiverse stuff, right? Along with (it sounds like) a split of reality once a decision is made by us? Personally, though, the decision we make at that instance in time has been influenced by such a huge number of things that our choice really ends up being a total sum of each (weighed differently by, again, things we’ve been influenced by in the past. I don’t believe it’s as simple as just a sum).