I can get that basic example to work if I update the package.json for the rescript/package.json and add this:
"exports": {
"./std/lib/es6/*": "./lib/es6/*", // add this
"./lib/es6/*": "./lib/es6/*",
"./lib/js/*": "./lib/js/*",
"./package.json": "./package.json"
},
The full app is still getting errors.