App for displaying 30s rolling average power
I'm not convinced you'll find an entirely satisfactory app, as most people who invest in a pricey power meter would tend to use a separate device such as this one
https://www8.garmin.com/manuals/webhelp/edge530/EN-US/GUID-53FC7978-187F-4E53-AA33-04853F86B05F.html
This app seems like it might have what you are looking for
https://www.jepster.nl/features.html
There don't seem to be too many users, but the app was recently updated (11 October) and the author seems to respond to feedback, so possibly if it's not quite what you want you might get improvements made!?