For those who are facing the same issue on ubuntu -> It seems there was an invisible window covering everything on my desktop, preventing me from clicking on other windows, files, text, and other items I needed to access. I searched for a solution and found some options. I had to visit several websites to find the perfect solution. In this article, I will compile all of them into one place. I'm still not sure how I got rid of it, but you should try the following.:-
Basic steps to follow
1. Do not panic Ü
2. Try Restarting or Logging out
3. Try changing the windowing system(X11, Wayland, Xorg) to another one and logging again with your default windowing system.
1st Solution - Use xkill command
xkill is a utility used for force-quitting GUI apps. It is handy when some app isn't responding or is causing your system to work abnormally.
Enter xkill in a terminal, or you can also press Alt+F2 to quickly access the command window. Your cursor will turn into a cross sign. Then click on the area you are unable to click or highlight. If it's a crashed application, that should terminate it.
If the above command didn't do anything try xkill -frame .
NOTE : This is a moderately dangerous command, use with caution.
2nd Solution - Use Process ID to kill it
To get the process ID, run xprop in a terminal. Your cursor will turn into a + sign (or something similar). Click on the problematic area to get the process ID.
Look for the line that says,
NETWM_PID(CARDINAL) = XXXX -> (xxxx will be the process PID and can be passed into the kill command)
Once you have the Process PID, open the terminal and run kill xxxx(replace xxxx with the process PID you've got), and it will forcefully kill the process ッ