how to block screen capture recording and Sharing of Libreoffice application into Ubuntu Linux?
Have you tried turning off your monitor and not turning it on? They say this is a very reliable way - even taking a picture of the screen using an external device (webcam or smartphone) is very difficult.And if you turn off the computer and will not turn it on, it will be impossible to get the contents of the screen by software and network means and existing files will be protected. What and from whom do you want to hide? Perhaps it’s easier to tell him “You shouldn’t look here”?
If you explain the context and reasoning, it may be possible to suggest some workaround.
There is the Respondus Lockdown Browser, which blocks this and more in an exam context. If you are prepared to pay for such a solution, you could ask them for a quote for adaptation to your setting. They do not offer it for open source platforms at the moment, so high price may be expected, if they are at all willing to do it.
You would probably need supervisor access (root/wheel/sudoers) to the Linux workstation to make it work. Also, the “analog loophole” (external camera) cannot be eliminated.