Yeah, I'm not saying that you're in the wrong, I'm saying that they might want to access further than the new `ACTION_OPEN_DOCUMENT_TREE` API call allows. For example, the Downloads folder (you can only open individual files with ACTION_OPEN_DOCUMENT, not the whole folder). And that can be reached with the `MANAGE_EXTERNAL_STORAGE` (all files) API. Is that OK? Well, it's not intrinsically bad, but it clashes with Google's Android hardening directives.
Not very familiar with the NextCloud client, as I haven't used it much, but in the case of Syncthing (and this is totally guessing from what I remember from reading the forums back when the Android 11 upgrade happened): I don't think they don't want to put the work to switch to the new API, I think they want to access places they won't be able to access with the new API, so that's why they won't change the calls.
Not very familiar with the NextCloud client, as I haven't used it much, but in the case of Syncthing (and this is totally guessing from what I remember from reading the forums back when the Android 11 upgrade happened): I don't think they don't want to put the work to switch to the new API, I think they want to access places they won't be able to access with the new API, so that's why they won't change the calls.