No, really. Let's stick to the example online banking: If you need to install software to use it, why don't you just deliver an Electron (like) application, and host the whole banking application inside of the application? You get the additional benefit, that you can configure the security inside your applications browser as you wish, pin certificates to make MITM even less likely. Electron let's you ship native code too, comes with an auto updater, etc.

And there are numerous alternatives to Electron if you don't like to ship a full Chrome browser. It get's a bit more complicated then, but its possible, take a look at Tauri for example.

To be honest, I had multiple projects, where a http://localhost solution was proposed, and we found a better solution without it. It is very rarely the best thing to do.