Cannot click on fedora AppVMs while using external display

I have a laptop with Qubes OS installed. After logging in, I connect it to a widescreen external display via an HDMI cable, and then activate that external display with something like arandr or xrandr --output HDMI-1 --auto. My ability to use both displays is hampered, however, when the displays are not mirrored:

  1. HDMI Display: I can only click on windows if they are on the left ~3/4 of the display, i.e. there is a vertical section on the right of the display to which windows can be moved, but on which my mouse cannot click those windows. The mouse instead seems to click along a vertical “virtual border” which seems to define the beginning of the unclickable section. I estimate that the unclickable section has dimensions (2560 - 1920) x 1080, i.e. I can only click on the 1920x1080 part of the widescreen, and not on the remaining part.

  2. Laptop Display: The mouse cannot click on fedora-based AppVMs. I can use the mouse on all dom0 windows, for example, as well as on whonix-ws-15 dvms, debian-10 based VMs, and fedora StandaloneVMs, but not on fedora AppVMs. I can use the keyboard on all VMs.

I use the i3 window manager now but can confirm this occurs on XFCE.

Case History and Details:

I used to plug in my HDMI cable after logging in to my user account. I discovered on accident that if I connect the HDMI cable not less than halfway through the post-LUKS boot process, then everything works. The login manager appears on the HDMI display (instead of on the laptop), and I can use the entire HDMI display, and all VMs are clickable on the laptop display.

Before today, only dom0 windows were clickable on my laptop display if I connected the HDMI cable after logging in. Today, however, I implemented a solution to another problem, which, given that it was a fix to a graphics driver, would seem to have probable cause in now allowing me click on debian/whonix-based VMs on my laptop display— but still not fedora VMs.

I have several separate questions:

  1. Why are fedora-based AppVMs the only unclickable VMs on my laptop display after connecting an external display?

  2. Why should connecting the display before the login manager make a difference? Is the gnome that handles external displays only on shift during boot?

  3. Why is only a 1920x1080 section of my 2560x1080 display accessible? Is there a good guide to something like xrandr that would fix the problem, or is this Qubes related?

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I think I’ve seen this type of problem myself. I wonder if it’s related to the initially reserved video RAM buffer size: GUI configuration | Qubes OS

If you want, you can try increasing the video RAM buffer to see if this addresses the issue.

Another update: when I place my HDMI monitor to the right of my laptop monitor, instead of above (what I’d always done before), no VM is limited in its clicking capacities. The widescreen monitor is clickable everywhere.

e.g. xrandr --output HDMI1 --right-of eDP1