It is not possible to easily edit subpages in the Talk namespace – which are often used for drafting revisions or layout changes – due to the nature in which the user interface reacts when being fed Talk namespace data from the API.
An example of such a page is this ancient relic found here:
https://en.wikipedia.org/wiki/Talk%3ANorfolk_State_University%2FNotes
The only way to edit is either via individual sections – assuming there are appropriate headers available to latch onto.
Or, being lucky enough to have an issue template/banner atop the page, which can then be clicked on, which will then expose an edit source option in the hamburger menu.
These are both dirty hacks.
If neither exist: there's no editing.
Also: if selecting 'Read article' from hamburger, it'll 404 as there is no article with that slash outside Talk.
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App version: (Beta) 2.7.50450-beta-2023-08-15
Pixel 6a; Android 13; SDK/API 33; August 2023 patches
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APK: https://github.com/wikimedia/apps-android-wikipedia/pull/4328