Using bookworm I have an install of Qt5 using apt-get. This is a new install, an older install this worked, but not now. QStrings show as an address in QtCreator debug window. Helpers are selected, but I believe it might be because the debug symbols are not available in the repositories.

I tried installing Qt from the online installer, but that has problems with crashing so I assume their arm installer is not qualified for the Raspberry pi.

Anyone have this working with Qt5.x?

After a few days of trying, including compiling Qt and Qt creator from source, which was marathon of finding and installing missing depencies, only to find QtCreator would crash when it launched. I was compiling Qt6.5 but had Qt5 installed from the repositories, so it was possibly getting confused.

In the end I created a fresh install of Pi OS 64bit, then download the Qt6 online installer.
These are the dependencies I installed first as a precaution. Some may already be available on Pi OS, but after suffering days of crashing because of missing components, I was trying to be cautious.

build-essential cmake ninja-build python3-dev
libxcb1 libx11-xcb1 libfontconfig1 libxrender1 \ libxcomposite1 libxcb-keysyms1 libxcb-image0 libxcb-shm0 \ libxcb-icccm4 libxcb-sync1 libxcb-xfixes0 libxcb-shape0 \ libxcb-randr0 libxcb-render-util0 libxcb-xinerama0 \ libegl1-mesa libglib2.0-0 libxi6 libsm6
libgles2-mesa libgl1-mesa-glx libopengl0

Before running the installer this should be installed
libgles2-mesa libgl1-mesa-glx libopengl0

I obtained the installer from the QT site - requires a logon account.

Running the installer, I selected custom install. Selected an older 6.x, then selected only the components I needed including the debug symbols.

The install proceeded smoothly, including the maintenace tool which will be useful in the future.

I now have a Qt install, including being added to the Programming Menu on the Start Menu. Debug symbols like QString are now correctly displayed.

All now seems to be working fine and I can continue with my programme on Qt6 making changes suggested from Qt5.

All this was on a Pi4 with 4Mb of memory. I have yet to try this on my Pi5 with 8Mb and SSD - but I had experienced the same initial crashing problems on the Pi.

It seems like the issue is probably due to missing debug symbols for Qt5, which is why QStrings are showing as addresses in the QtCreator debug window. Since the online installer isn't working on your Raspberry Pi, you might want to check if Qt5 with debug symbols is available in your distro's repo or try building Qt5 from source with debugging enabled.