Security best practices for Flutter Web

I am working on a Flutter web/Firebase app and have been researching security best practices to build into the app. My app will allow users to enter text for their profiles and will also have an embedded chat function where free text can be added. I want to prevent potential attacks but in my research I have not found specific suggestions or best practices to address these risks for Flutter web. I have implemented Firebase security rules and have experimented with using a validator on a TextFormField to flag XSS-related characters/strings, but am looking for a more comprehensive set of measures. Can anyone suggest sources for this guidance? Thanks.