I do have a problem with encrypted Dropbox files.
I have added Dropbox as an external service some time ago. The files that Nextcloud saved to the Dropbox are encrypted. Some time ago, Dropbox dropped the OAuth v1 support, resulting in my Nextcloud not being able to mount the Dropbox storage anymore. How can I decrypt the files that are stored on the Dropbox without having to mount it within Nextcloud?
There is no dedicated decryption tool. I have asked for it some time ago (https://github.com/owncloud/core/issues/13591) but it was never put in place. I found a repo which says it can do it: https://github.com/Leryan/owncloud-decrypt (not sure if it works with current NC versions).
Perhaps you can somehow copy it on local storage, and also keep the database-entries in the same version (a signature is derived from the database and restoring without the same database version is not possible, except you disable the signature check (not sure how easy that is).
@bjoern can you help?
If you don’t get an answer, please open an issue on the bug tracker on github.com/nextcloud/server/issues. I think this can be a critical issue like your case shows. You also might want to recover single files from a backup, currently you only can restore the whole setup (or perhaps one user account).
Install Dropbox V2 and reconnect your Dropbox. Maybe you will get access to your files:
The App works for me
I have tried adding the Dropbox with the suggested app. The Dropbox is connected again, but the files are still not accessible.
I will file a bug report, as encryption without the ability to decrypt is the best way of deleting files.
Did you done a rescan with occ? Maybe this solves it. Otherwise feel free to open a bug report, because this might help other people to decrypt the files, if something will be wrong with nextcloud in future