Thanks @v-bacao-msft .
I have posted in Forms forum. Hopefully, someone can get back to me soon.
Surprisingly, the Form trigger can pick up all the surveys/quiz created in multiple environments. As I only have a quiz created in the default environment, this trigger can pick it up, and this flow works as well.
I can use Form connector for Form Pro as well, as the quiz I mentioned above is actually created in Form Pro. However, there are only two actions from Form Pro.
Another trouble is how I can get a final score or individual question score via a flow.
Thanks.