--- qt-everywhere-src-6.8.3.old/qtbase/src/corelib/io/qdataurl.cpp
+++ qt-everywhere-src-6.8.3/qtbase/src/corelib/io/qdataurl.cpp
@@ -47,10 +47,10 @@
         QLatin1StringView textPlain;
         constexpr auto charset = "charset"_L1;
         if (QLatin1StringView{data}.startsWith(charset, Qt::CaseInsensitive)) {
-            qsizetype i = charset.size();
-            while (data.at(i) == ' ')
-                ++i;
-            if (data.at(i) == '=')
+            QByteArrayView copy = data.sliced(charset.size());
+            while (copy.startsWith(' '))
+                copy.slice(1);
+            if (copy.startsWith('='))
                 textPlain = "text/plain;"_L1;
         }