*Note: Password for the archive is 'pcgw' 
This patch removes the black bars during cutscenes for ultrawide users.
Simply locate the 'witcher3.exe' file and hit apply. Next time you're in a cutscene the black bars should be gone.  
Just let me know if the patch isn't working for you, I'll try to fix it. 

This is an official patch made by Cyan. Uploaded here to make it easier to find since this was only posted in a forum.
From: https://forums.cyan.com/viewtopic.php?f=83&t=1587
As of December 29 2020, This is still newer than the gog and steam versions.
==Original Description==
 

*Note: Password for the archive is 'pcgw'
Made a patcher for Ashen that corrects FOV for 21:9 and 32:9 users. 
Extract the archive, run the patcher and locate Ashen-Win64-Shipping.exe then click 'Start' on the patcher. 

*Note: Password for the archive is 'pcgw'
Turned the fix from Code Vein's PCGW's hex editing ultrawide guide into a patcher. I don't take credit for the actual hex-editing work. All I did was correct the FOV and implement the hex edits from the ultrawide guide into a patcher so it's easier to apply for those who don't want to hex edit things themselves. 
In-short this patch removes the black pillars from cutscenes and corrects the field of view for 21x9 and 32x9.
Extract the archive, run the patcher and locate CodeVein-Win64-Shipping.exe then click 'Start' on the patcher.