This might help? It is a button thing, you've to assign first and 2nd action (if you like) and it can activate the sheet or website etc.. and second action helps you to other actions too...
The above extension won't trigger upon opening of the sheet but selection of a button. I don't think we have triggers in Qlik Sense but in Qlik View.
This extension has multiple actions/trigger support:
Vizlib Text Object:
I am sure you can slightly modify it to run on open rather than on click.