Détecter Windows 11 en JavaScript :

async function isWin11orLater() {

    let reponse = false;

    if (navigator && navigator.userAgentData) {
                await navigator.userAgentData.getHighEntropyValues(["platformVersion"])
                .then(ua => {
                    if (navigator.userAgentData.platform === "Windows") {
                        const majorPlatformVersion = parseInt(ua.platformVersion.split('.')[0]);
                        if (majorPlatformVersion >= 13) {
                            //alert("Windows 11 or later");
                            reponse = true;
                        } else {
                            reponse = false;
                        }

                    }
                    else {
                        reponse = false;
                    }
                });
    }

    return reponse;
}


(async function() {
    const test = await isWin11orLater();
    if (test)
        alert("is Windows 11 or + : true");
    else
        alert('is Windows 11 or + : false')

})();

Compatibilités des navigateurs en Mai 2022

Documentation : https://docs.microsoft.com/en-us/microsoft-edge/web-platform/how-to-detect-win11

Documentation : https://developer.mozilla.org/en-US/docs/Web/API/Navigator/userAgentData