"Zusi 3 - Aerosoft Edition" includes the "ZusiDisplay" application which is affected: https://store.steampowered.com/app/1040730/ZUSI_3__Aerosoft_Edition/

It can be a bit difficult to get running. I believe you need to manually install dotnet core (there's an installscript_netcore.vdf, but it only works if you rename it to installscript.vdf apparently), and you need the micross.ttf font, but I believe a replacement for that font is now in the Proton distribution (even though the font metrics are slightly off, so the ZusiDisplay settings menu has no visible buttons at the bottom).

The main application (Zusi) then has a menu entry to launch ZusiDisplay (in German: Konfiguration -> ZusiDisplay starten -> ZusiDisplay Grundmaske starten), which usually triggers the crash for me while closing the small loading screen window. It feels a bit racy though, like sometimes it works when starting it again directly after a crash. Just adding the UiaDisconnectProvider stub to Proton's 6.3 wine code, building the uiautomationcore.dll and putting it into the "dist/lib/wine" Proton directory works reliably for me so far (while building the dll from proton-6.3 branch unchanged and using that file will crash ZusiDisplay).

Something inside ZusiDisplay then apparently hides the useful exception shown in the upstream bug report and reports another exception instead (probably because the original exception is thrown inside a thread and the usual "show exception message from a thread" user interface is not available at this stage of the application initialization - see the "OnThreadException" method in the callstack), which is

Unhandled exception. System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection. (Parameter 'index')
   at System.Collections.ArrayList.get_Item(Int32 index)
   at System.Windows.Forms.FormCollection.get_Item(Int32 index)
   at MMI.Program.Application_ThreadException(Object sender, ThreadExceptionEventArgs e)
   at System.Windows.Forms.Application.ThreadContext.OnThreadException(Exception t)
   at System.Windows.Forms.Timer.TimerNativeWindow.OnThreadException(Exception e)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
   at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
   at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
   at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
   at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
   at System.Windows.Forms.Application.Run(Form mainForm)
   at MMI.Program.Main(String[] args)