I don't know how I manage to sort my files and folders as 'Last modified', but anyway, I wasn't able to sort back on 'Name'.
In Finder, there is a difference between 'Sort by' and 'Arrange by'.
Column view - click 1 file - RMB (Right Mouse Button) -> you have a menu
Column view - click 1 file - Hold alt-option- button + RMB (Right Mouse Button) -> you have another menu. You see 'Arrange by'
Let go the alt-option button and the menu changes to 'Sort by'
(Same in the top menu and preferences)