After upgrading from 6.12.88-1 to 6.12.90-2, display mirroring (clone mode)
no longer works on GNOME/Wayland. The external display is detected and
works in extended mode, but mirroring cannot be activated via GNOME
Settings → Displays.
Reverting to 6.12.88-1 resolves the issue.

Hardware:
- Lenovo ThinkPad T14 Gen 5 AMD
- AMD Ryzen 7040 series (Phoenix), amdgpu driver
- External display via HDMI

Software:
- Debian 13 (Trixie)
- GNOME on Wayland
- Kernel 6.12.90+deb13.1-amd64 (broken)
- Kernel 6.12.88+deb13-amd64 (working)

Relevant dmesg error:
ucsi_acpi USBC000:00: ucsi_handle_connector_change: GET_CONNECTOR_STATUS failed (-110)

Control: tags -1 + moreinfo upstream

Can you please bisect the changes between 6.12.88 and 6.12.90 upstream
to identify the breaking commit? That would involve compiling and
testing a few kernels:

    git clone --single-branch -b linux-6.12.y https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
    cd linux-stable
    git checkout v6.12.88
    cp /boot/config-$(uname -r) .config
    yes '' | make localmodconfig
    make savedefconfig
    mv defconfig arch/x86/configs/my_defconfig

    # test 6.12.88 to ensure this is "good"
    make my_defconfig
    make -j $(nproc) bindeb-pkg
    ... install the resulting .deb package and confirm problem does not exist

    # test 6.12.90 to ensure this is "bad"
    git checkout v6.12.90
    make my_defconfig
    make -j $(nproc) bindeb-pkg
    ... install the resulting .deb package and confirm problem exists

With that confirmed, the bisection can start:

    git bisect start
    git bisect good v6.12.88
    git bisect bad v6.12.90

In each bisection step git checks out a state between the oldest
known-bad and the newest known-good commit. In each step test using:

    make my_defconfig
    make -j $(nproc) bindeb-pkg
    ... install, try to boot / verify if problem exists

and if the problem is hit run:

    git bisect bad

and if the problem doesn't trigger run:

    git bisect good

. Please pay attention to always select the just built kernel for
booting, it won't always be the default kernel picked up by grub.

Iterate until git announces to have identified the first bad commit.

Then provide the output of

    git bisect log

In the course of the bisection you might have to uninstall previous
kernels again to not exhaust the disk space in /boot. Also in the end
uninstall all self-built kernels again.

Regards,
Salvatore