DomPDF: iconv(): Wrong charset, conversion from `utf-8' to `us-ascii//TRANSLIT' is not allowed

Laravel Project: 7.6.1

DomPdf: 0.8.7

I've created a function to generate a pdf from a html file. This function is loaded at the click of a button.

First time, I put my css directly in my html page and there was no problem. But now, I would like to put it in an external file.

Now, when I click on the button, I've the error:

iconv(): Wrong charset, conversion from `utf-8' to `us-ascii//TRANSLIT' is not allowed

Head of my Html

<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
    <title>Laravel PDF</title>
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.0/css/bootstrap.min.css">

    <link href="./css/app.css" rel="stylesheet">
    <script src="./js/chart/report.js" ></script>

    <style>
        @page { margin: 100px 25px; }
    </style>
</head>

My controller

$pdf = PDF::loadView('report.pdf.index-pdf', compact('datas'));
$pdf->setPaper('A4', 'p');

return $pdf->download('report.pdf');

Somebody to help me?