I think this tutorial isn't up to date anymore.

I think this tutorial isn't up to date anymore. Can't find "Thank you page" on the Settings page.

It seems you may have been comparing a Card form with the instructions mentioned in this guide. Please note that in Card forms, this customization is not possible and the Thank you page is not present in the Form Settings, but in the form builder at the bottom of the form:

Hope this clarifies.