Thank @Etresoft!, I would have liked to add some pics to the post, but as we can't do that, I will try to explain more carefully. I created a really simple application that uses the fullwidth style with 1 column with a table view cell that only draws its background. When debugging the view with the Xcode hierarchical debug button, I can see that the cell is not occupying the entire tableview row view. There is still some padding horizontally on both sides. When I debug using 12.1, the cell occupies all the row correctly. I will try the .plain style as @galad87 says but I think I already tried it without any luck. I have a question on an external website with pictures attached named: How to remove NSTableView indentation on Big Sur that includes the example app and the screenshots. Thanks again !

Appreciate it.

Just adding that this is also happening with Xcode 12.1 store version with BigSur 11.0 Beta (20A5395g)