Hello ...
I saw a post in the wsgf Doom 2016 thread by ... HWGuy ... that showed a fix for Doom after an update that stopped the original plugin from working.
It's here ... https://www.wsgf.org/phpBB3/viewtopic.php?f=61&t=30953&start=160 Thank you HWGuy.
So following what he did I did the same and used Flawless Widescreen's Wolfenstein II's plugin with a slightly changed script for Doom Eternal and it worked in game ... the menu background does not get fixed with this.
The changed WolfensteinII.lua script is attached below.
Here is what I changed ...
Near the start of the script is this section ...
--PROCESS VARS
Process_FriendlyName = Module:GetFriendlyName()
Process_WindowName = "Wolfenstein II The New Colossusx64vk"
Process_ClassName = "Wolfenstein II The New Colossus"
Process_EXEName = "NewColossus_x64vk.exe"
I changed it to ...
--PROCESS VARS
Process_FriendlyName = Module:GetFriendlyName()
Process_WindowName = "DOOMEternal"
Process_ClassName = "*"
Process_EXEName = "DOOMEternalx64vk.exe"
So just drop the downloaded WolfensteinII.lua script here ...
C:\Program Files (x86)\Flawless Widescreen\PluginCache\FWS_Plugins\Modules\WolfensteinII\Dependencies\Scripts
Run Flawless widescreen with the Wolfenstein II plugin for Doom Eternal.
Enjoy.
I don't have enough knowledge to make a full/proper plugin for Flawless widescreen so hopefully someone that knows what they are doing can make one using this info.
It works for multi-monitor too.