Must use import to load ES Module: /home/semaphore/LibreLingo/node_modules/rehype-format/index.js require() of ES modules is not supported. require() of /home/semaphore/LibreLingo/node_modules/rehype-format/index.js from /home/semaphore/LibreLingo/apps/web/__sapper__/build/server/server.js is an ES module file as it is a .js file whose nearest parent package.json contains "type": "module" which defines all .js files in that package scope as ES modules. Instead rename index.js to end in .cjs, change the requiring code to use import(), or remove "type": "module" from /home/semaphore/LibreLingo/node_modules/rehype-format/package.json.