Hey @kimyoungjin1001
Looking at the package.json at the root of the repository and that in packages/frontend I see no build script, only a start script. This command in turn runs netlify dev which is not something you run when deploying to Netlify, it is a Netlify CLI command used when developing locally.
As explained in this post npm start won’t work on Netlify. The idea is you deploy a static site (built with something like Eleventy which I see you are using) or an SPA built with React, Vue, et.al. which is done via a build script or other build command.