Version 1.06 of Red Dead Redemption 2 was mostly meant to add updates to Read Dead Online, but many players are reporting that the update has removed ambient occlusion from the game. Although changes to graphics are not mentioned in the patch notes, several players have posted screenshots from version 1.0 and 1.06 that show definite changes in lighting.
Ambient occlusion plays a big part in a game being able to render lighting realistically. It's what allows some games to render lighting based on the actual geometry of a room or item. Ambient occlusion finds where the lighting source is and blocks out light where an object, person, etc. would be in the way.
The first report of graphics changes came from Twitter user Darealbandicoot, who posted side by side screenshots of a bar scene in version 1.0 and 1.06. Although the changes are small, and some people made comments that they couldn't tell the difference, the shadows around the bar and on Arthur's jacket are less rich and dynamic.
The differences can be seen more easily by zooming in on shadowed areas.
Rockstar's patch notes for version 1.06 don't mention anything about graphic changes, aside from some small texture changes, so it seems strange that ambient occlusion would be removed completely. It's possible that the differences are caused by players going through the same scenes in different weather or at different times of day.
It's also possible that ambient occlusion was removed accidentally when other changes were made, which means the issue will likely be fixed in a future update.
Hopefully, the screenshots are just unfortunately timed, and ambient occlusion is not gone for good. One of the reasons why Red Dead Redemption 2 has been so well received is because of its excellent graphics, especially its visual immersiveness and attention to detail. As some players have said, the differences can be hard to see for the average gamer, but those who are well-versed in the technical side of games will no doubt be disappointed in this visual downgrade.
Those who want to avoid the update should avoid connecting their game to the internet to prevent it from downloading patches. If your game has already updated, just uninstall and reinstall it without an internet connection.