I have a Canon gx7 mark ii. whenever i go to film it’s black tv like lines going through the viewfinder and when i go to look at the videos on my laptop the black lines are still there. No idea how to fix it or where they even came from. please help.
If the lines are appearing in both, it is possible that the sensor has failed. Can you take a stills photos of something and see if the lines are still there, please? By checking that it is impacting both functions it gives us some more detail to work with.
Have you done any updates to the system, changed settings or in any way impacted the camera recently?
That is encouraging. It suggests the sensor itself is not damaged. It seems to me that you have some kind of configuration error. So, I would suggest that you first check that you are using the correct video format and settings. If they appear to be in order, then the next thing to do is perform a full camera reset.
This is detailed on P 176 of your manual which, if you have not got that, is available from THIS LINK