You are right. You can do the build process in two ways:
Automatic using hollaex web
Manual through npm run build as you mentioned
Keep in mind that if you use the manual build you need to set your server address for the client server to connect to in the .env variable called REACT_APP_SERVER_ENDPOINT
Once you run the build there will be a build folder in your project that you can use and host anywhere.
For more information please read the guideline here.