Here is what I've found so far but I'm not an expert...
1a. Use Cheatengine :
- Replace 1.777777791 (float/Address 140F482A0) by 2.333333254 to change aspect ratio.
- Replace 41800000 (hex, 4 Bytes/Address 140F48320) by 41A8000 to fix a problem with ghost shadows.
Or 1b. Hexedit the .exe directly :
- Search and replace the second (I insist) 39 8E E3 3F by 55 55 15 40
- Search 00 00 80 41 (It's the one just after 39 8E E3 3F ) and replace it by 00 00 A8 41
2. Open graphics.ini in LOCAL DISK:\Users\YOUR NAME\AppData\Roaming\Sega\Yakuza0 and replace numbers by the following :
Letterbox=0
UIOffsetX="0.000"
UIOffsetY="0.000"
UIScaleX="0.800"
UIScaleY="1.000"
TargetAspectX=21
TargetAspectY=9
And that's all !
There is one problem with this method : All USM files (Pre-rendered movies) located in Program Files (x86)\Steam\steamapps\common\Yakuza 0\media\data\movie_w64 are STRETCHED.
I tried to correct the ratio by re-encoding them with Vidsquish
https://steamcommunity.com/groups/vidsquish/ by changing a profile and it worked (letterboxed or cropped) but I can't figure out a way to add audio...