The programming you can access online will depend on what system the TV uses to do that.
If it's a Roku TV then you can add Roku channels to it. In addition to the ones you can download directly there are private channels that require you to enter a code to access. You can do a Google search.
If you have an Android TV then any Android apps will work.
Many smart TVs have their own app stores so you are limited to the ones you can download.
Many people use KODI which can be downloaded or sideloaded onto a variety of streamers. Some content is legal some is not.