You can select any file you could before on shared external storage. You can't select private app directories which were always off limits from other apps just like on iOS.
From what I see (and what I've experienced on different sync apps when upgrading Android versions, although I'm not a developer, just a user), access to /Android/data and /Android/obb changed on Android 11:
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[0] On Android 11 (API level 30) and higher, you cannot use the ACTION_OPEN_DOCUMENT_TREE intent action to request access to the following directories:
- The root directory of the internal storage volume.
- The root directory of each SD card volume that the device manufacturer considers to be reliable, regardless of whether the card is emulated or removable. A reliable volume is one that an app can successfully access most of the time.
- The Download directory.
Furthermore, on Android 11 (API level 30) and higher, you cannot use the ACTION_OPEN_DOCUMENT_TREE intent action to request that the user select individual files from the following directories:
- The Android/data/ directory and all subdirectories.
- The Android/obb/ directory and all subdirectories.
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[1] On Android 11 (API level 30) and higher, you cannot use the ACTION_OPEN_DOCUMENT intent action to request that the user select individual files from the following directories:
- The Android/data/ directory and all subdirectories.
- The Android/obb/ directory and all subdirectories.
Yeah, yeah, I know. I'm not saying that it's good or bad, I just say that some people like to sync/backup/copy their apps data (that sometimes it's located on private directories, or in the Downloads folder...), and they were able to do it before. And that the new API has less permissions than the one that Google wants them to use.
Google Play, or at least that's what they say in their docs, might allow the use of the MANAGE_EXTERNAL_STORAGE "all files" API call "...if your app includes a use case similar to any of the following: File managers, Backup and restore apps, [...] Document management apps ..." [0][1]. And the Nextcloud app sounds very similar to that.
Of course, it's all "Subject to Google Play review and approval.", but why they used to grant that permission to Nextcloud with no problem and revoked it suddenly... I have no idea.
Note that `MANAGE_EXTERNAL_STORAGE` permission doesn't allow access to /Android anymore either (it's blocked by OS permisisons) so it won't help Nextcloud to retain it either.
Thing is, Nextcloud doesn't need that permission since they can do what they do now with SAF which is how Google determines eligibility for the exception. That is - if you can do it with SAF, you don't need complete access to all private data via MANAGE permission.
You can select any file you could before on shared external storage. You can't select private app directories which were always off limits from other apps just like on iOS.