Ok, I figured it out. As I can't use insecure WebSocket inside the WKWebView if I am in HTTPS (what I want), the best option is to get rid completely of the WebSocket server and to use WKScriptMessage instead which allows to send JavaScript to native code in a WKWebView. Furthermore, we get rid of networking issues we can have with the WebSocket server and since iOS 14, when we are receiving some JavaScript calls from WKWebView, we can also provide a response easily with a reply handler. Thanks for the help.

Thank you for your prompt reply. Okay, I see, but I can't use insecure WebSocket if I am in the WKWebView with HTTPS because of mixed-content, correct ? By does the work, you mean using WKScriptMessage to communicate with the javascript from the web page in the web view and communicate with my WebSocket server underneath or completely get rid of the WebSocket server ? Thanks. Christophe