This is a backwards incompatibility in the library itself. PHP 8.1 no longer allows autovivification of false-y values

PHP natively allows for autovivification (auto-creation of arrays from falsey values). This feature is very useful and used in a lot of PHP projects, especially if the variable is undefined. However, there is a little oddity that allows creating an array from a false and null value.

And they give this example

// From false
$arr = false;
$arr[] = 2;

I went and found the file in question and this is the function it's in

function ServerInfo() {
    global $ADODB_FETCH_MODE;
    static $arr = false;
    if (is_array($arr))
        return $arr;
    if ($this->fetchMode === false) {
        $savem = $ADODB_FETCH_MODE;
        $ADODB_FETCH_MODE = ADODB_FETCH_NUM;
    } elseif ($this->fetchMode >=0 && $this->fetchMode <=2) {
        $savem = $this->fetchMode;
    } else
        $savem = $this->SetFetchMode(ADODB_FETCH_NUM);

    $arrServerInfo = sqlsrv_server_info($this->_connectionID);
    $ADODB_FETCH_MODE = $savem;
    $arr['description'] = $arrServerInfo['SQLServerName'].' connected to '.$arrServerInfo['CurrentDatabase'];
    $arr['version'] = $arrServerInfo['SQLServerVersion'];//ADOConnection::_findvers($arr['description']);
    return $arr;
}

The problem is that it starts with

static $arr = false;

and then tries to autovivificate a non-array (line 154 in your error)

$arr['description'] = $arrServerInfo['SQLServerName'].' connected to '.$arrServerInfo['CurrentDatabase'];

You should be able to fix it (in theory) by making sure it's an array (something they should have done anyways). Add this above that line to make it one before it tries to append

if(!is_array($arr)) $arr = [];