There's been a thread since 2020 from another user about this topic, and the fact that the AGOL/Enterprise team @ ESRI haven't bothered to address this basic ability feels insanely bothersome. I know because I replied to it in 2024. Well, here we are at the end of 2025 and this VERY basic request seems to be ignored.
Link to topic: https://community.esri.com/t5/arcgis-dashboards-ideas/duplicate-delete-group-stack-dashboards-inc-be...
Basically what they suggested:

Because once again, I am tasked with creating numerous mobile versions of our dashboard that my peers want for public viewing. What's currently aggravating is unless I'm completely blind, why can't we at least move the stack selector to the top of our stacks?

As you can see in Dashboard Creator/Experience builder, this is still forced to the bottom. It's a simple request.