Help understanding the UX logic of synch in android app

I am using nextcloud for almost 2 years on my desktops and servers without any particular problem.

But on the same time I am having a bit of trouble understanding the UX logic behind the Android app.

I can not seem to find a way to trigger synch any one folder structure from the app .
Uploading files yes, but synching folders ?
The instant upload seems to upload only NEW created files ,and with the file or folder option I have to manually select files .
Isn’t the whole point of nextcloud is Folder sharing / synching and not file uploading ?
On the UX level - why can’t I just select a list of folders to synch ?
An I missing something here ?