I am migrating over to using the new app bridge instead of the embedded SDK and can't seem to find how to replicate a feature I made use of in the embedded SDK.
I was able to open a modal specifying a path to the page to load in the iframe - when one of the action buttons is clicked I was then able to call a function in the iframe page e.g.
This would allow me to put a form in the modal, allow the user to enter something and then capture that and use it, in my case to update some settings.
Does the ability to do this no longer exist in app bridge?
I literally looked into this yesterday as I too am trying to port an older app.
I discovered this - https://shopify.dev/tools/app-bridge/actions/modal#communicate-with-the-parent-page - which seems to solve it!