Description of problem:
Using HTTP.php, I get the following error:
PHP Fatal error:  Array and string offset access syntax with curly braces is no longer supported

The error is at line 500 and following:

        if (!strlen($url) || $url{0} == '#') {
            $url = $uriAll.$url;
        } elseif ($url{0} == '?') {
            $url = $uriBase.$url;
        }
        if ($url{0} == '/') {
            return $server . $url;
        }

Since PHP7.4, Curly Braces is not suppoorted.

How to fix:
Replace url{0} with url[0] in code.

For information, HTTP2 has superseeded HTTP but has the same issue.