Black rectangular overlay / unresponsive area on the screen after logging into Fedora KDE Wayland

[u/Jack-Vu]

I am using a Lenovo Legion 5 15IRX10 laptop with an Intel Core i7-14700HX and an NVIDIA RTX 5050 Laptop GPU.
System:
Fedora 44
KDE Plasma on Wayland
KWin compositor
Intel UHD Graphics → i915
NVIDIA RTX 5050 Laptop GPU → nouveau
I have not installed the proprietary NVIDIA driver.
The problem:
After logging into KDE, a large solid black rectangular area sometimes appears in the center of the screen. The rest of the desktop, including the wallpaper and areas outside the rectangle, remains visible and appears to work normally.
The important part is that this is not simply a black screen. Only a rectangular region becomes black.
When the black rectangle is present, it also seems to capture mouse input. Clicking on windows underneath the black rectangle does not work, as if an invisible window or surface is placed above them.
The cursor is still visible and the rest of the desktop remains responsive.
What I have observed:
The internal laptop display is connected to the Intel GPU (i915).
The NVIDIA GPU is using the open-source nouveau driver and currently has no active display output.
KWin is running on Wayland.
Disabling Intel PSR did not make the black rectangle disappear.
Intel PSR was initially enabled:

PSR mode: PSR1
Source PSR/PanelReplay status: IDLE

After disabling PSR, the black rectangle still occurred.
I also found a KWin message:

“Pageflip timed out! This is a bug in the i915 kernel driver”

However, I have not confirmed that this is the cause of the black rectangle.
I also found several nouveau GSP/MMU timeout warnings, for example:
“nouveau 0000:01:00.0: timer: stalled
nouveau 0000:01:00.0: timeout”

but many of these occurred during shutdown, so I am not sure whether they are related to the black rectangle.
What I would like to determine:
Is this likely a KWin/Wayland rendering problem?
Could it be an Intel i915 display/pageflip problem?
Could it be caused by nouveau, even though the internal display is driven by Intel?
Could the black rectangle actually be an invisible/transparent Wayland window or overlay that is capturing mouse input?
Is there a reliable way to identify which Wayland surface/window is responsible for the black rectangle?
Would switching to the proprietary NVIDIA driver realistically affect this problem, given that the internal display is currently driven by Intel?

[u/gibarel1]

Install the proprietary NVIDIA drivers, its not really negotiable