A description of the problem:
In the newly installed Centos7.9, when logging in as root in the graphical interface, "sorry, that didn't work please try again", as shown in the following figure:
It has been confirmed that the root password is correct. After all, it is possible to log in under the command line of the terminal.
Two solutions For
this problem, the solution is to reset the root password.
Type in terminal:
# sudo passwd root
Then enter the original password, and then confirm the password, you can.
As shown in the figure below:
After entering the root password again in the graphical interface, you can log in normally.