iOS NC App - only view files - don't download/synch

Long story short:
How can I VIEW files in my nextcloud app on my iOS device WITHOUT DOWNLOADING, storing and synching the actual file to my iOS device - or at least have them deleted locally after viewing.

Hello everyone,
I am running a nextcloud installation on a raspberry pi to replace my drobpox usage.

RPi is setup with:
Nextcloud version: 20.0.2 (nextcloudpi)
Operating system and version: Linux 5.4.51-v8+ aarch64 (rasbperrypi)
PHP version: 7.3.19

I setup everything and us a MacBookPro for synching my entire data with the nextcloudpi instance, which is working perfectly fine. For my mobile device, I want use it as view only - i.e. not synch all my data to my mobile device.

I am using
Device: iPhone 7
OS: iOS 14.3
App: Nextcloud Coherence for iOS

With Dropbox it was easy to access my data via the dropbox app and open files within the app, e.g. a *.pdf file. From my understanding the files are NOT downloaded to the device to view them - or at last are remove again afterwards.

For the nextcloud app however, if I click a *.pdf file in my nextcloud space, the file is downloaded and marked with a green circle and checkmark. The 3 dots next to the file also offer the option “mark for offline availability” (i.e. the file was not yet marked as such).

How can I achieve this dropbox like behavior?

Thanks for your help!