How to use Gmail app without any browsers installed?
Android apps can make use of a WebView (web browser that runs inside the app).
Depending on the Android version Google preferred used Chrome webbrowser app to provide this WebView or the Chrome based WebView app.
Any other WebView capable web browser can also be used.
Go to Settings -&gt; System -&gt; Developer options -&gt; WebView implementation to see and select the app that provide the WebView to all apps.

In your case the WebView app may be the best to install because it can't be used as stand-alone web browser but once installed GMail app should work again as it provides the necessary WebView component.