1. Remove gdm3 and gnome-shell, while removing gnome-shell it was showing something 'polkit-1-auth-agent is not installed so not to remove'
2. Install gnome-shell, gdm3, policykit-1-gnome, also ubuntu-gnome-desktop and ubuntu-gnome-default-settings
3. Enable debugging gdm3 (/etc/gdm3/custom.conf file), Moved all files from /var/crash, and reboot the system. No login screen but no files in /var/crash
4. Reboot into recovery mode and run journalctl -b-1 > boot1.txt
I did further more steps,
1. Remove gdm3 and gnome-shell, while removing gnome-shell it was showing something 'polkit- 1-auth- agent is not installed so not to remove'
2. Install gnome-shell, gdm3, policykit-1-gnome, also ubuntu- gnome-desktop and ubuntu- gnome-default- settings
3. Enable debugging gdm3 (/etc/gdm3/ custom. conf file), Moved all files from /var/crash, and reboot the system. No login screen but no files in /var/crash
4. Reboot into recovery mode and run journalctl -b-1 > boot1.txt