Note that this is a non-official backport which required a bit
of adaptation to work with 6.10.3, seems to work but possible
overlooked something.

https://bugs.gentoo.org/973374
https://codereview.qt-project.org/c/qt%2Fqtdeclarative/+/733089
--- a/src/qml/qml/qqmltypecompiler.cpp
+++ b/src/qml/qml/qqmltypecompiler.cpp
@@ -5,4 +5,5 @@
 #include "qqmltypecompiler_p.h"
 
+#include <iterator>
 #include <private/qqmlobjectcreator_p.h>
 #include <private/qqmlcustomparser_p.h>
@@ -919,13 +920,12 @@
     // Apply the ordering in the IR
     obj->setFirstAlias(ordered[0]);
-    if (ordered[0] == defaultPropertyAlias)
-        obj->indexOfDefaultPropertyOrAlias = 0;
-    for (qsizetype i = 0, end = ordered.size() - 1; i < end; ++i) {
+    for (qsizetype i = 0, end = ordered.size() - 1; i < end; ++i)
         ordered[i]->next = ordered[i + 1];
-        if (ordered[i] == defaultPropertyAlias)
-            obj->indexOfDefaultPropertyOrAlias = i;
-    }
     ordered.last()->next = nullptr;
 
+    if (defaultPropertyAlias) {
+        auto it = std::find(ordered.constBegin(), ordered.constEnd(), defaultPropertyAlias);
+        obj->indexOfDefaultPropertyOrAlias = std::distance(ordered.constBegin(), it);
+    }
     return true;
 }