setTimeout(() => {

        // fuck up all future javascripts

        setTimeout = setInterval = requestAnimationFrame = () => {};
        Element.prototype.appendChild = () => { throw new Error("Blocked"); };
        document.addEventListener = () => {};
        window.addEventListener = () => {};
        Object.defineProperty(document, "readyState", { get: () => { throw new Error("No JS"); } });
        document.write = () => {};

        // fuck up canvas
        if(window.HTMLCanvasElement) HTMLCanvasElement.prototype.getContext=()=>null; 

        // fuck up webgl
        if(window.WebGLRenderingContext) window.WebGLRenderingContext.prototype.getParameter=function(){e=>{throw new Error("Blocked")}};

        // fuck up webgl2
        if(window.WebGL2RenderingContext) window.WebGL2RenderingContext.prototype.getParameter=function(){e=>{throw new Error("Blocked")}};

        // fuck up websockets
        window.WebSocket=function(){e=>{throw new Error("Blocked")}}; window.EventSource=function(){e=>{throw new Error("Blocked")}};

        // fuck up popups
        window.open=()=>null;

        // ...

    }, 500);

    const iframe = document.createElement("iframe");
    document.body.append(iframe);
    iframe.contentWindow...

    javascript:(function () {
        const rm = () => document.querySelectorAll('iframe')
            .forEach(f => f.remove());
        let timeout;
        const debouncedRm = () => {
            clearTimeout(timeout);
            timeout = setTimeout(rm, 100);
        };
        rm();
        new MutationObserver(debouncedRm)
            .observe(document.body, {
                childList: true, subtree: true
            });
    })();

By farbling I mean making the data look like it's the most common Windows configuration, for example.

You will have messed up layouts and unneeded quirks. Moreover, banks are using fingerprinting to detect fraud so you will have a hard time on those websites as well.

And more importantly.

https://xkcd.com/1105/

Of course I wouldn't farble on my bank's website, that would be pretty stupid.

But by default I would want trackers to get the farbled data, and only allowlist the websites I trust. Same trust concept as with uBlock Origin, NoScript and others.

Nah, this is just straight up false. Many pages work fine with NoScript blocking all scripts. For those that don't, you usually only have to allowlist the root domain, but you can still leave the other 32 domains they are importing blocked. It's actually surprisingly common for blocking JS to result in a better experience than leaving it enabled (eg no popups, no videos, getting rid of fade-ins and other stupid animations).

I won't argue if you think that is too much work, and I definitely wouldn't recommend it for a non-technical user, but it's not nearly as bad as you described.

I wasn't clear, but this is about my experience. Maybe you are in a different bubble. But I'm not able to book a hotel, browse GitHub, file my taxes, make a bank transfer or even look up the menu of a restaurant.

The only exceptions for me are HN and a handful of news websites.