Can iOS apps request updated permission to selected photos?
It looks like this is a limitation of the Twitter app, not the SDK:

3) Showing the selection UI again
the recommended way is to manually request to show the selection UI again. Apple explains that if you have an app that requires full access to the photo library (e.g. some app whose main purpose is to let you browse and organize the photo library), you should add some kind of button in your UI that triggers the selection screen again.

https://mackuba.eu/2020/07/07/photo-library-changes-ios-14/

As further evidence that this is a limitation of the app, Facebook provides a dialog that allows me to select additional photos: