[Bug 50102] New: [5.20 regression] Starcraft fails to download cloud settings in fullscreen mode

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=50102

Bug ID: 50102
           Summary: [5.20 regression] Starcraft fails to download cloud
                    settings in fullscreen mode
           Product: Wine
           Version: 5.20
          Hardware: x86-64
               URL: https://www.blizzard.com/en-us/download/confirmation?p
                    latform=windows&product=scr
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: -unknown
          Assignee: [e-mail]
          Reporter: [e-mail]
   Regression SHA1: 859b526c81a2af841b5b7b28d06f3d782bccdab5
      Distribution: ArchLinux

Since 5.20, when logging into Starcraft (either from Battle.net App, or by
manually launching the exe and clicking "Login"), after the message
"Downloading Settings" is displayed the game freezes for a moment and then
shows "Download failed".

Bisection gives:

859b526c81a2af841b5b7b28d06f3d782bccdab5 is the first bad commit
commit 859b526c81a2af841b5b7b28d06f3d782bccdab5
Author: Jacek Caban 
Date:   Mon Oct 12 18:27:18 2020 +0200

kernelbase: Use conhost in AllocConsole.

I've compared 12cc863a4a5 and 859b526c81a, both with applied
winebuild-pe_syscall_thunks Staging patchset (needed because of bug 42741).
Startup is as follows:
1. Loading screen shows;
2. Main menu shows with the message "Authenticating";
3. Message changes to "Downloading Settings";
4. The screen goes blank for 2 seconds, like when changing resolutions;

Then on 12cc863a4a5:
5. When the screen is back up, all messages are gone and the game is fully
functional.

But on 859b526c81a:
5. When the screen is back up the game is frozen (animations in the background
are not played);
6. After another 2 seconds the message "Download failed" is displayed and the
game unfreezes. There is a rare chance that "Download failed" will not be shown
and the game just unfreezes, but most of the time the message will show up.

This is only happening in "Fullscreen" and "Windowed (Fullscreen)" modes in the
game's video settings. With "Windowed" mode, point #4 above does not apply (the
screen doesn't go blank), the game doesn't freeze and there is no "Download
failed" message.

If I enable "Emulate a virtual desktop" option (while setting the game to
fullscreen) then it's kind of in-between: the game freezes for about 5 seconds
when displaying "Downloading Settings", but after that the "Download failed"
message does not show up.

I'm using a dual-monitor setup, AMD RX 570, Arch Linux with KDE Plasma.