If anyone ends up here, I found this to be working. I played for few hours now without issues and cutscenes are finally looking amazing.

https://www.reddit.com/r/widescreengamingforum/comments/jqxq8c/assassins_creed_valhalla_219_cutscene_fix_no/

I've found this solution here on forum, so search sometimes do helps.
Here is oryginal post:
https://discussions.ubisoft.com/topic/77520/21-9-32-9-support-for-cutscenes

Also ... Ubisoft - I guess in terms of widescreen support, your games are somewhat DIY

Cheers!

OMG! How long it will take for devs to STOP ADDING black bloxes to cutscenes? This is actually MORE WORK to add them, why not just LEAVE everything native? Can't wrap my head around it, where is this "feature" comming from? What is a technical limitation on our state of the art, Real Time Ray Tracing graphics cards and Next Generation graphics ENGINES that require you to crop image ?

Can we PLEASE stop this nonsense already !?

Does anyone know any workaround to have normal 21:9 image available in game ?

GAME LOOKS ABSOLUTELY AWFUL !!!