The first argument needs to not be a character type with Qt 6.9.

--- scribus-1.7.0/scribus/util_text.cpp	2025-01-25 21:57:41.000000000 +0000
+++ scribus-1.7.0/scribus/util_text.cpp	2025-04-04 10:30:28.988262041 +0100
@@ -100,7 +100,7 @@
 	QString out;
 
 	for (auto c : text)
-		out += QString("U+%1,").arg(c.unicode(), 4, 16, QChar('0')).toUpper();
+		out += QString("U+%1,").arg(long(c.unicode()), 4, 16, QChar('0')).toUpper();
 
 	return out.mid(0, out.length() -1);