Nextcloud ONLYOFFICE Powerpoint Full Screen Watermark NOT displayed


I have installed NEXTCLOUD (latest stable version) with ONLYOFFICE (latest stable version), I have activated the watermark on all shared links that is working fine with the browser for XLSX, DOCX, PPTX, PDF. Now if I try to access by a mobile device (ipad,iphone safari) the powerpoint presentation has an option to switch to full screen (PLAY button -> not available by PC/Webbrowser). If I press the Play button the watermark is not displayed in FULL screen mode.

Is this a bug ?
Is it possible to disable the play button (full screen mode) completly independant from the device ?

Thank you,