The new CloudFlare JS Challenge via POST request minimal solution.

cf_post_challenge.js

// Before executing, make a break point on "#jschl_answer" element so when it gets a value, debugger kicks in...
(function() {
    let form = document.querySelector("#challenge-form");
    if (!form)
        return console.log("No JS Challenge detected!");

    let request = function(params, callbackFn) {
        fetch(params.requestURL, {
            "method": "POST",
            "headers": {
                "content-type": "application/x-www-form-urlencoded",
            },
            "body": `r=${params.r}&jschl_vc=${params.jschl_vc}&pass=${params.pass}&jschl_answer=${params.jschl_answer}`,
        }).then(res => res.text()).then(res => {
            callbackFn(res);
        });
    };

    let solveChallenge = function(htmlResponse) {
        let doc = new DOMParser().parseFromString(htmlResponse, 'text/html');

        let operation = doc.head.innerHTML.match(new RegExp("setTimeout\\(function\\(\\)\\{\\s+(var (?:\\w,)+f.+?\\r?\\n[\\s\\S]+?a\\.value =.+?)\\r?\\n"));
        operation = operation[1]
            .replace(new RegExp("a\\.value = (.+ \\+ t\\.length.+?)\'?;.+", "g"), "$1")
            .replace(new RegExp("(e\\s=\\sfunction\\(s\\)\\s\\{.*?};)", "gms"), "")
            .replace(new RegExp("\\s{3,}[a-z](?: = |\\.).+", "g"), "")
            .replace("t.length", (location.host.length + 1).toString())
            .replace("\\n", "");

        return {
            "requestURL": doc.querySelector("#challenge-form").action,
            "r": doc.querySelector("input[name=r]").value,
            "jschl_vc": doc.querySelector("input[name=jschl_vc]").value,
            "pass": doc.querySelector("input[name=pass]").value,
            "jschl_answer": eval(operation.toString()),
        };
    };

    // Disable form submit functions, so it doesn't automatically redirect the browser page (since we want do confirm everything works manually)
    form.submit = function() {};

    let bypass = function(currentHTML) {
        request(solveChallenge(currentHTML), function(responseHTML) {
            setTimeout(() => {
                bypass(responseHTML);
            }, 5000);
        });
    };

    // Function that takes a document HTML string as input and calculates the solution which is then used for comparison to see if both solutions are identical
    // This was mainly used for confirming cloudflare bypass implementation calculations on other languages (like Kotlin)...  
    let testSolution = function(testHTML) {
        let current = {
            "requestURL": document.querySelector("#challenge-form").action,
            "r": document.querySelector("input[name=r]").value,
            "jschl_vc": document.querySelector("input[name=jschl_vc]").value,
            "pass": document.querySelector("input[name=pass]").value,
            "jschl_answer": document.querySelector("#jschl-answer").value,
        };

        let solved = solveChallenge(testHTML || document.documentElement.innerHTML);
        return [current, solved];
    };

    bypass(document.documentElement.innerHTML);
})();

The gist of how CF challenge works in pretty details - https://stackoverflow.com/a/60131975