Vue Cli 3 project won't generate manifest.json (PWA)
I had the same issue. I ran a production build: yarn build or npm build and found the manifest.json file in the dist folder.
try Adding manifest.json manually under public file or you can also copy the manifest.json generated after npm build under the dist folder into the public file and then edit it according to your needs. Also check if your browser is detecting the manifest.json or not.
vue add @vue/pwa
vue create <app-name>
manifest.json is located in public folder, not in src