Not able to login as a root or normal user after configuring root file system read only in RHEL7.6 server
 

1) Was trying to configure root file system in read only mode in newly installed RHEL 7.6 server with default configuration using below mentioned link:
https://access.redhat.com/solutions/2196881
2) After rebooting the system, could not login as either root or normal user. However gdm login screen appears with username and password prompt.
Please note that /etc/fstab file contains default configuration before making any changes.

This looks like a RHEL-specific solution. I would ask Red Hat Support.

Not able to login as a root or normal user after configuring root file system read only in RHEL7.6 server
 

Do you have /home and /root on a different filesystem?

No.
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Below are contents of /etc/fstab

/dev/mapper/rhel-root / xfs defaults 0 0
UUID=5e095ac5-864a-4205-aa1f-dc9774b7f5df /boot xfs defaults 0 0
/dev/mapper/rhel-swap swap swap defaults 0 0

Have you tried to log in from a virtual console (e.g. Ctrl+Alt+F3) and watch error messages?