Mirroring Displays Doesn't Mirror Them

Distribution

Fedora Linux 41

Package version

6.4.6

Graphics hardware in use

Intel Corporation CoffeeLake-H GT2 [UHD Graphics 630]

Frequency

Always

Bug description

If I try to mirror 2 displays, it doesn't mirror. I just get a streak across the top of 1 display.

Steps to reproduce

1. Start Linux, with monitor hooked up by hdmi cable.
2. Plug in tablet with usb-c to mini hdmi cable.
3. Start Monitor app on tablet.
4. Open Displays.
5. Start Mirroring. Mirroring does not mirror. If I have an open window on the monitor, as large as possible, I may get a streak across the top of the tablet.
6. Try to change scaling on the tablet, in case it's a resolution issue.
7. Select the tablet under Display, and change user interface scaling for the tablet.
8. Instead it changes user interface scaling on the monitor, and then crashes, leaving me in fallback mode.

Possibly related to https://github.com/linuxmint/cinnamon/issues/12415

I suspect that would affect other pairs where the minimum resolution for one device exceeds the maximum resolution for the other.

Expected behavior

If I mirror 2 displays, they should mirror. If I can't mirror them, at least provide a warning, or gray out the mirror button.

Additional information

No response

Start by reproducing the issue in Fedora Linux 41 with the Intel UHD Graphics 630 and the HDMI/USB-C display setup described. Inspect the Displays mirroring and per-display scaling behavior, using the related issue #12415 as context. Done means mirroring either works for the two displays or the UI warns or disables mirroring when the resolutions are incompatible, without changing the wrong display or crashing.