I’m assuming that you changed your user’s Default Homepage option to Categories. Unless a user has explicitly set their Default Homepage option, their homepage will be the homepage that is set by the top menu site setting.
If you have access to your site’s Rails console, you could reset all of your user’s Default Homepage settings so that it will be set based on your top menu setting. To do that, enter the Rails console and run:
UserOption.update_all(homepage_id: nil)
If you are unsure about running this command, I would just not do it. It is likely that most or all of your users will already have their Default Homepage set to Latest.