I know how to set up the autosplitter in the settings, but I am having trouble downloading the autosplitter from a site that has it. I don't know if I did something wrong or missed something, but this is the link to the site.
Here's the direct link to the script (right-click and Save As to a safe place, then add a Scriptable Auto Splitter component to your layout): https://raw.githubusercontent.com/periwinkle9/cave-story-autosplitters/main/cave-story-combined.asl
I've also been meaning to add this autosplitter to the official list of autosplitters that LiveSplit can automatically download from the Edit Splits window, which would make setting this up much simpler. However, I've only really tested it with the freeware game so far so I'd want to make sure that it actually works with Cave Story+ before I do that. (I see no reason why it wouldn't work, but I haven't gotten around to verifying that yet.)