You can use the Firebase Storage Extension by Mirxtrem
https://community.appybuilder.com/t/firebase-storage-v2-0-new-features/18869 - That page doesn’t exist -
Extension is here:
https://community.appinventor.mit.edu/t/firebase-storage-extension/58184/2
with example here:
or do it all with the web component and webviewer (REST/WEB)
Firebase Storage with Web Component
If you want to use secure rules then:
https://ai2.metricrat.co.uk/guides/firebase-authentication-with-web-component-and-html
or