Ios iphone (not: ipad) app previewing .docx files as photos

when I open a file of the .docx (MS word) type on my iphone (iOS 17.2) it is being displayed as a photo with a grey image placeholder now.
This did work nicely in the past.
And to make it more strange, it still works nicely on an ipadOS 17.2 ipad. This makes me believe the server side is fine.
NC is version 27.1.3.
Other office type documents like xslx and pptx display their previews nicely as well.

I wonder if there is any setting anywhere which influences how some filetyoes are being treated.

I already did both an app reset and de-/new install.

What Office platform are you utilizing server-side?

Anything weird under Settings->Advanced->Capabilities when compared between the working and non-working devices?

I assume the client app versions are the same?