QFileInfo and UTF-8

Question

I am having trouble getting QFileInfo to work with UTF-8 paths.
I am on Ubuntu 20.04.
While std::filesystem has no issue with the (in this case) German UTF-8, it seems QFileInfo is not using UTF-8, even though the Qt documentation says the default encoding is unicode (https://doc.qt.io/qt-5/qtextcodec.html)

EDIT: before the example with the file,here is a simpler example. This example shows that QString is not the issue, but rather the settings that influence the Qt I/O:

QString temp {"Höhe.txt"};
qDebug()<<"Qt temp: "<<temp;
std::cout<<"Qt through std: "<<temp.toStdString()<<std::endl;
std::string str = temp.toStdString();
std::cout<<"std: "<<str<<std::endl;

results:

Qt temp:  "Hhe.txt"
Qt through std: Höhe.txt
std: Höhe.txt

So, qDebug() is omitting the 'Ö' while the QString::toStdString() delivers the full string correctly.

Here is a distilled example code: In all cases below std::filesystem finds the file, but Qt doesn't see it.
The qDebug() output is always without the 'Ö' - it is simply 'Hhe.txt'
NOTE: my real code is not using string literals - the below string literal is only used for the example to keep things simple.

#include <QFileInfo>
#include <QtDebug>
#include <QTextCodec>
#include <filesystem>

int main(int argc, char **argv)
{
    std::filesystem::path p{"Höhe.txt"};
    //QFileInfo f(p.c_str()); 
    //QFileInfo f(std::filesystem::u8path(p.c_str()).c_str());
    //QFileInfo f(QString::fromUtf8(std::filesystem::u8path(p.c_str()).c_str()));
    QByteArray encodedString = "Höhe.txt";
    QTextCodec *codec = QTextCodec::codecForName("UTF-8");
    //QString file = codec->toUnicode(encodedString);
    QString file = QString::fromUtf8(encodedString);
    QFileInfo f(file);
    if(!std::filesystem::exists(p)) {
        return 1;
    }
    if(!f.exists()) {
        qDebug()<<f.filePath(); //outputs 'Hhe.txt' for all cases
        return 1;
    }
    
   std::cout<<"found"<<std::endl;
   return 0;
 }

Can anyone help me get QFileInfo to also be able to see files with unicode characters?

Many thanks in advance!

Some additional information (as per questions in the comments):

~$ locale
LANG=C
LANGUAGE=en:el
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_PAPER="en_US.UTF-8"
LC_NAME="en_US.UTF-8"
LC_ADDRESS="en_US.UTF-8"
LC_TELEPHONE="en_US.UTF-8"
LC_MEASUREMENT="en_US.UTF-8"
LC_IDENTIFICATION="en_US.UTF-8"
LC_ALL=en_US.UTF-8

My system however generally, has no issue showing German text, be in console or UIs..

and

$ ls Höhe.txt | od -t c
0000000   c   h   i   n   e   s   e   .   e   x   t  \n   c   z   e   c
0000020   h   .   e   x   t  \n   d   u   t   c   h   .   e   x   t  \n
0000040   e   n   g   l   i   s   h   _   u   k   .   e   x   t  \n   f
0000060   i   n   n   i   s   h   .   e   x   t  \n   f   r   e   n   c
0000100   h   .   e   x   t  \n   g   e   r   m   a   n   .   e   x   t
0000120  \n   g   r   e   e   k   .   e   x   t  \n   i   t   a   l   i
0000140   a   n   .   e   x   t  \n   j   a   p   a   n   e   s   e   .
0000160   e   x   t  \n   p   o   l   i   s   h   .   e   x   t  \n   p
0000200   o   r   t   u   g   u   e   s   e   .   e   x   t  \n   s   p
0000220   a   n   i   s   h   .   e   x   t  \n   s   w   e   d   i   s
0000240   h   .   e   x   t  \n   t   u   r   k   i   s   h   .   e   x
0000260   t  \n
0000262

And:

main.cpp: C source, UTF-8 Unicode text

Answer 1

The comments from n.m. were on the right track. The issue is not in the code, as I originally thought but the locale configuration on my system.

The output of:

 QTextCodec::codecForLocale()->name().toStdString();

is 'System'.
I am not sure what 'System' is configured to though.
And setting Qt Locale on UTF-8 explicitly:

QTextCodec::setCodecForLocale(QTextCodec::codecForName("UTF-8"));

Made the code work correctly on my system as well.
This means that the issue is in the Locale configuration of my system.
So I have to figure out what is wrong with my Locale, but that is a different question.

Many thanks to all of you who helped!!