Does Google Drive have this elevated privilege? If so, seems blatant abuse of app store control. If not, it would seem to indicate there is a workaround somehow the Nextcloud could also leverage.
Drive doesn't sync arbitrary files on Android though. A closer analogue to what nextcloud is trying to do would be syncthing, who also discontinued its Android app due to issues with getting the proper permissions with the play store (see https://github.com/syncthing/syncthing-android/issues/2064).
