So it seems to be related to the fullscreen hack, Proton-GE was built without it for some time and only got it re-enabled in the latest update. With that latest update, things broke on there as well.

Also haven't been able to use virtual desktop for quite some time, I wonder if this is some weird unique configuration quirk we share? There's a distinct lack of noise about this that I would otherwise expect considering how long it's been broken.

I have the same problem, when I launch a game with a virtual desktop, it is getting stuck in the right part of the screen.
Is there any progress on this issue, or is it abandoned?

So it seems to be related to the fullscreen hack, Proton-GE was built without it for some time and only got it re-enabled in the latest update. With that latest update, things broke on there as well.

Do you know what version Proton-GE that fs-hack was still disabled because Im interested in trying it as Proton 5.0 is a bit old and I would like to game on Virtual Desktop with a more recent version if its possible?

Am building proton, how does one disable fs-hack and other settings in general when configuring a build with proton?

After lots of testing, I did find a working workaround for this: I am on Linux Mint, and on a 3 monitor setup, setting my leftmost monitor as primary! display in Linux, allows me to successfully run Proton/Steam games with Wine virtual desktop spanning all 3 monitors, game window correctly aligned in virtual desktop.

I combine this with switching to compiz display manager (cause that one allows me to force the desktop size to 6020x1080), and a pre-run script in lutris that sets the virtual desktop size within wine prefix through registry, e.g. like:

# [...]
if [[ "_$game_name" == "_Elite: Dangerous" ]]; then

    export WINE="/home/user/.local/share/Steam/steamapps/common/Proton - Experimental/files/bin/wine"
    export WINEPREFIX="/data3/SteamLibrary/steamapps/compatdata/359320/pfx"

    # Gets the current, full resolution
    RES=`xdpyinfo | awk '/dimensions/ {print $2}'`

    cat > temp.reg << EOF
REGEDIT4
[HKEY_CURRENT_USER\Software\Wine\Explorer]
"Desktop"="Default"
[HKEY_CURRENT_USER\Software\Wine\Explorer\Desktops]
"Default"="${RES}"
[HKEY_CURRENT_USER\Software\Wine\X11 Driver]
"GrabFullscreen"="N"
EOF

    "$WINE" regedit temp.reg
    rm temp.reg
fi
# [...]

Sadly, Steam input does not get forwarded to that window :( my flight stick works directly through linux, but my DS4 controller doesn't.

I would be so fantastic!, if Proton would offer a PROTON_ALL_DISPLAYS=1 switch as mentioned in #5213 :D ..then in combination with compiz (or with a feature request to Cinnamon to support all monitor fullscreen windows..), we could simply fire up a (non virtual desktop) fullscreen wine window with the full 3 monitor resolution \o/

@bobbadshy Thank you! Setting my leftmost monitor as primary worked.

Is there any progress on this issue other than choosing the left monitor as a primary (which messes my workflow in other applications)?

I personally stopped caring about this long ago and just use gamescope instead. Only leaving the issue open since others appear to care.

I personally stopped caring about this long ago and just use gamescope instead. Only leaving the issue open since others appear to care.

Even if they didn't this is still a valid bug. Sometimes I must use Virtual Desktop because in some cases applications can't properly query information about their other windows. Additionally, for some games Virtual Desktop has been beneficial to compatibility or performance in some way, and, I do sometimes wish it were working correctly in Proton because of this.