I uninstalled gnome by mistake!

[Dixit]

Ya that problem

[Elegant_Emperor]

@Dixit

I think I should change to gdm

Repeat the process and make your mind..

sudo dpkg-reconfigure gdm3

and choose gdm3 from the prompt.

[Dixit]

I told that cuz error is still there

[Dixit]

Reload failed

[Elegant_Emperor]

sudo systemctl start gdm3.service  

Try this.
and then:

sudo dpkg-reconfigure gdm3

[Aravisian]

I wonder if the GDM files are changed, since you tried to install gnome 40 or 41 (There is a gdm.41)
Try removing and purging GDM3, then reinstalling it from the Zorin Repos

[Michel]

sudo -i

Try to login as root and try the above commands to see if it makes any difference.

[Dixit]

[Elegant_Emperor]

I did not refer to that command.

sudo systemctl start gdm3.service

and use sudo
or simply get root access as @Michel said, by using sudo -i

[Dixit]

When I use this command

sudo systemctl start gdm3.service

What shoud I do?

[Elegant_Emperor]

@Elegant_Emperor

and then:

sudo dpkg-reconfigure gdm3

Did you reconfigure gdm?

[Dixit]

No buttons are working

[Aravisian]

Your screenshot shows that a symlink may be the issue.
You may need to remove the display-manager.service symlink, then run the command.

[Dixit]

Try is available

[Michel]

If it was my system i would start from scratch and do a full wipe and reinstall. You made a mess of it and installed things on it you did not know what it would do with the system.

[Elegant_Emperor]

Or BACKUP! FOR GOD'S SAKE PEOPLE CREATE A BACKUP!

[Aravisian]

Seconded on both suggestions above... It is likely other files were corrupted or altered during the attempt to install Gnome40.
The above commands simply should have worked.

[Dixit]

Ok , I have dual booted ubuntu I will take the backup and then re install it

[Elegant_Emperor]

@Aravisian

It is likely other files

Takes time to hunt them, doesn'it?