I would likely need to see your weback.mix.js file to be more helpful but from the first line of the error message: ...The provided value "public" is not an absolute pat... it looks like somewhere in your webpack.mix.js you're providing a relative path and webpack is looking for an absolute path. So taking a look at the webpath.mix.js file that comes with spark, at the top it pulls in the path module:
var path = require('path');
and later in the file when getting the spark js files it resolves a relative path to an absolute path:
path.resolve(__dirname, 'vendor/laravel/spark/resources/assets/js'),