This is an issue I have been trying to fix for a while now, I am running Kubuntu 20.04 and whenever I put my laptop to sleep or close the lid and try to wake it up again the LED's at the back of the screen turn on (as well as the fans), but there is no login screen.
I have to then manually shut down my laptop then restart it, go through the GRUB menu, select Kubuntu and then go to the login screen
My laptop = Hp Laptop 15-db0xxx (Ryzen 5 2500u with Radeon Vega 8 Moblie Graphics)
I have also tried implementing the solutions below but they did not work:
18.04 Screen remains blank after wake up from suspend
https://www.reddit.com/r/linux4noobs/comments/f58f2w/kubuntu_1910_black_screen_after_sleep/
Best Answer
Had the same problem, running Kubuntu 20.04 with 2 users configuration, on 2nd user after running a game I will have a black or frozeen scren after wakeup. On the old days Kubuntu had by default configured a hot key sequence to kill the X server Ctrl+Alt+backspace. I activated the hotkey sequence in system settings and it works for me. Go to System Settings,Hardware, Input Devices, Keyboard, advance, find "key sequence to kill X server" and select Ctrl+Alt+backspace. Hope this work for you too.