Thymeleaf HTML File Support

I'm trying to get the the Thymeleaf support to work as mentioned on this page https://www.jetbrains.com/help/idea/thymeleaf.html

I've done everything on this page applicable and yet it is still not working. What am I missing here?

For context, its a very simple app, Spring Boot with Thymeleaf. I have the most recent version of IDEA