Can't see "available offline" on android

On android I have some files that have a little white circle with a green tick. These seem to be “available offline” files that also appear if I go to the “on device” tab.

However if I right click these files, or the directory, I can’t see an option to toggle these “available offline”, nor can I make other directories or files “available offline”. It’s like the button is just missing.

Here is a screenshot of the context menu:

In my android file system I notice there is a separate directory in Android/media/com.nextcloud.client/nextcloud/ that has my offline files.

I have mixed success of pressing sync to get things to appear here. And I don’t seem to be able to remove things from this by pressing “sync” again.