Starting May 2021 app updates on Google Play must target at least Android-11.
Android-11 brings into effect some important restriction on how apps can access the files, in particular apps cannot read files in the external storage created by other apps.

TopoDroid can create its base folder, and populate it with the survey database, sketch files, and all the rest. However if the app is uninstalled and later reinstalled these files "belong" to a different app, and are no longer accessible by TopoDroid.
In this case the app signal a "Stale TopoDroid folder".

The way to go about this is to rename the old "TopoDroid" folder with another name, and restart TopoDroid. It will create a new "TopoDroid" folder

It is important to make zip archives of all the surveys, and save them in a safe place, before uninstalling the app. By this means surveys can be restored inside the new "TopoDroid" folder, from the archives.

Ife the zip archive was not created, it is still possible to make it with one of the following Linux scripts:
zip5.sh for TopoDroid v.5 folder
zip6.sh for TopoDroid v.6 folder

First copy the "TopoDroid" data folder to a Linux machine. Next run the script from the "TopoDroid" folder. Without arguments the script lists the surveys in the TopoDroid database. With argument a survey name, it creates the zip archive.