@Retr0djmarky The createFile method is on the env that you create from https://www.npmjs.com/package/@typescript/vfs (not on env.languageService).
For custom types, I think it’d be best to upload your types to a CDN and then download them lazily when your editor loads.
FWIW My implementation is also public now, if you want to take a look: https://github.com/prisma/text-editors/