I was typing a document-- suddenly the task bar with bold,underline etc disappeared. A huge, intrusive New Theme bar with pictures is now at the top of every new page.
It’s simply the Image Gallery
To hide it click on the menu Tools > Gallery (7th item)
Choose Tools - Gallery or on Standard Bar, click the Gallery icon
Click the button on the edge of the docked window to show or hide the docked window…
This looks to me like a malware. Did you run a virus check on your machine?
Which OS and LibO version are you using?