Until last night I was using Ubuntu's default Windows environment. I don't know which Ubuntu's desktop was that. Maybe it was GDM.

Last night I installed KDE Plasma Desktop via Terminal. I did not like it. So I uninstalled it and came back to Ubuntu's default desktop. Everything is the same again. But the lock screen has become like the picture below it has never been before.

This lockscreen hangs a lot. It doesn't take me to the desktop even after entering the password. Even the keyboard mouse doesn't work. I can enter by turning off the PC and turning it on again.

What kind of problem is it? How can I solve it?

Note: My OS Ubuntu 20.04

My PC

Intel core i3 10 Generation

RAM 8 GB

SDD 120 GB

Gigabyte H410M H V2 motherboard

This lock screen was not there before..