Late-breaking findings:

Per testing, the ADB command referenced in Android docs for enabling All 
Files Access for testing does not seem to work on Termux or Pydroid 3:

    adb shell appops set --uid PACKAGE_NAME MANAGE_EXTERNAL_STORAGE allow

This may require apps to declare the new permission in their manifest, 
though this hasn't been verified (and Android's fragmentation makes 
guesswork perilous; some behavior is device specific).  See the related
Mergeall note and reddit thread:

    https://learning-python.com/mergeall-android11-updates.html#allfilesaccess

    https://www.reddit.com/r/androiddev/comments/mscu80/as_a_user_is_it_possible_for_me_to_grant_an_old/

If this worked, it would be another route to enabling Mergeall's 
direct GUI syncs on Android 11, but it appears to be unusable.
It also may be less user friendly than the two-script runs of 
this package, but that depends on the user.

However, users can apparently toggle apps into legacy (i.e., pre-
scoped-storage) mode via ADB:

    https://forum.xda-developers.com/t/disabling-scoped-storage-via-adb-on-note-10-updated-to-android-11.4221617/

Termux and Python apps like Pydroid 3 are still in legacy mode, but 
this _may_ help if they ever move on from it.  The doc's storage 
overview still applies broadly; most apps can access shared storage 
in Android 11 with the same simple permissions dialog they used in
earlier Androids.