Pornhub even has a hidden Roku channel. You have to add hidden channels manually through your Roku account on a computer by a code #. Go to the Roku website, click on the settings icon (the round purple icon on the upper right with the human in it), then click on 'my account'. Sign into your account and scroll down to 'manage account' and click 'add a channel with a code'. Enter the code {Pornhub] with no brackets, and that's it. The Pornhub app will appear on your Roku device pretty quickly.
There are more hidden Roku channels. Some free, some pay. Just Google "hidden roku channels" and there are several sites with lists and codes. '