I discovered a possibly usable software solution to the problem discussed in Open Source File manager that can access app data folders? .
There is a system component com.android.documentsui.files.Files Activity, which is a an activity, and if you manage to launch it, such as by using this or that (the later is a very simple but innovative app I discovered recently), you gain access to a built-in file manager (like the file picker) which can access Android/data on one’s phone, bypassing the said restriction. (Experience may vary depending on one’s device manufacturer, as described in its GitHub page.)