When I tried to open it in Unity by clicking the “open in Unity” button, only my Unity editor was opened. There was no error message or anything. I also didn’t see the project in the project list
I have installed Unity Editor version 2020.3.38f1.
do you mean only Hub was opened, but not unity editor itself?
(the project wont appear in the hub projects list)
probably need to login into Hub first,
and if you create empty project, you can download your purchased assets while inside the unity project,
from Package manager. (clicking “open in unity” should also open the package manager, and have your asset selected,
then can press Import)