Here in my environment the same thing happened when trying to install the Ubuntu updates, the screen just went black then the prompt kept flashing and when I restart the machine the terminal is displayed but the graphical environment is not displayed, searching on the Net I see that it is a problem that affected many people around the world, as the cause was generated by an update released by canonical, I believe that only they can solve it
Here in my environment the same thing happened when trying to install the Ubuntu updates, the screen just went black then the prompt kept flashing and when I restart the machine the terminal is displayed but the graphical environment is not displayed, searching on the Net I see that it is a problem that affected many people around the world, as the cause was generated by an update released by canonical, I believe that only they can solve it