The solution itself is not that much - go to the website, do inspect, and go to the console tab to see the flag (or execute the javascript code at the end of the html file).
The [writeup](https://github.com/babaiserror/ctf/tree/main/%5B210723-27%5D%20ImaginaryCTF%202021/Roos%20World) includes the process of trying to figure out how the jsfuck code works.