We are running a Nextcloud instance configured to use an S3 object‐store as primary storage. All user files are stored in the S3 bucket as opaque objects (e.g. urn:oid:<fileid>).
Our organization plans to retire Nextcloud, we need a reliable, automated way to extract every user’s data into a standard, plain filesystem hierarchy (e.g. /backup/<username>/<folders>).
What is the migration path off the Nextcloud platform?
there is no. You should understand what data exists and how you want use this data later. Ask for support of the application you plan to use afterwards. you can export user data manually and transform to a desired format. app user_miration is more intended to move data between two servers but might help as well.
Possibilities that come to mind:
user_migration app should support S3 Primary Storage just fine. As an admin, you can use it for all users via occ user:exportocc files commands (copy/etc)