Hide Next button

Hello,

I am trying to change the state of the next button in a few instances on my slides in my story but encountering issues.

Issue 1: I want the next button to be disabled until a certain object enters the screen. But when they re-visit, it goes back to "hidden". How do I fix this even after I set to "Resume Saved State"

Issue 2: I want the next button to be disabled until the user clicks on buttons - which takes them to a layer. When they return, I want the next button to show. Do I need to create a trigger on each layer or just the main slide? Do i need to create a variable as well?

Thanks in advance!