Pour le 21:9
So, as far as Doom 2016 goes, the only fix (latest as of the day the forums where archived) I found was to downgrade with some older game files, then launch flawless widescreen using a custom .lua file that was uploaded by Helifax. I think this should work for you, since I couldn't get it working as well without the downgrade.
Try this: https://www.dropbox.com/s/avkzh292krrc5uk/DOOM.zip?dl=0
There's an image called instructions.jpg, just follow it to downgrade doom.
Then download the doom extensions file for flawless widescreen. https://www.dropbox.com/s/0s6ljpkog7g0w96/DOOM.lua?dl=0
Make sure to replace the doom.lua in \Flawless Widescreen\PluginCache\FWS_Plugins\Modules\DOOM\Dependencies\Scripts
Once replaced, run Flawless, start doom, then enjoy as that's the only way to get doom working as of the March 2018 patch.
Credited to the forum archives, most fixes not listed on the website or reddit forums are in there...a lot of user threads with unlisted fixes.
+ mod https://community.pcgamingwiki.com/files/file/1817-doomlegacymod-v201901/
