The Webview automatically opening when you run your Repl has been a confusing experience to many Extension developers since the beginning.
In all Extension Repls, the Webview will still exist in the Tools dock but will no longer automatically open upon running your Repl.
Quoting from the docs:
What’s the difference between the Webview and an Extension?
The webview is a normal iframe that displays the web output of your Repl. In the case of an extension, a special handshake is established between it and the Replit workspace.