This means they forgot platforms other than Windows exists. It’s likely they’re checking for currently supported systems and anything older is insecure, so blocked for your security.

Likely something like this pseudocode

function isPlatformVersionSupported(useragent) {
    // Windows XP is NT 5.1
    // Windows Vista is NT 6.0
    // Windows 7 is NT 6.1
    // Windows 8 is NT 6.2
    // Windows 8.1 is NT 6.3
    // Windows 10 and 11 is NT 10.0
    if (useragent.name == "Windows" && useragent.version.match(/Windows NT (6\.3|10)/)) {
        return true
    }

    // TODO: insert supported macos versions here

    return false
}