While Generating Android App this issue is faced by some users when your icon image is not of 512x512 px in size.
The + Icon will not appear in your PWA because of many reasons. There are 2 files required for PWA,
Manifest : manifest.json : https://vibethemes.com/manifest.json
Service Worker : firebase-messaging-sw.js : example : https://vibethemes.com//firebase-messaging-sw.js?v=0.0002
Both are located in your website root. So you should be able to access them like above links for vibethemes.com
Possible reasons for PWA not working :
Missing Service worker file
Missing Icons in Manifest.json
Scope mismatch of manifest and serviceworker
Huge Page and loading times
Each of these have a different debug method and for 1,2,3,4 you can attempt re-generating the service worker from WP admin - Vibebp - Settings- BuddyPress but in general to debug you have to open your site in chrome browser and look for errors in Application :
When Service Worker is enabled in Vibebp - Settings - General. You are not able to edit the pages in Elementor. This happens as the service worker caches scripts and Elementor is not able to work properly. The quick fix is to unregister the service worker on the page while editing in elementor.
After clicking Unregister, reload the page and your page starts loading normally. This will work with all the page builders(whatever you are using).