test Oracle linux creation , asking login password after installation ... screenshot attached

Where's the Problem? you are logged in as root! The Installer itself has the option where you set the root Password as well as create a separate User & give him a Password. Both of those are towards the bottom Left of the installer Window where you also select all other options.

i want to get  GUI after reboot
..not getting that 

yes .. You are right.
I choose all the defaults. That's why it chose the minimum facility.
As advised, from the screen  you mentioned  in the screen, when I did the customization of all the configuration appeared all set right.

Now a perfect VM. Working good.

In Linux it is common to not install too much.  For server environments a GUI on the console is useless at best. (one never uses the console really, most of the time server setups are in lights out DC's. or even virtualized)  Often GUI software is too complex and large to audit so it is presumed to be full of security holes.

@noci,
the installation I did  home lab.. in order to explore  all features..
Thank you for your recommendation with respect to that. 

VM looks good ...Please advice ...
I want to add a new disk for dedicated partition - /dev/sdb ... which would be the best file system to choose ext4 or xfs for Oracle-Linux 7.9 release. 

Although XFS may have some advantages over Ext4, Those probably aren't relevant in most cases, so in my point of view it doesn't really matter. If your OS Disk uses Ext4, I'd use the same for the 2nd disk, to make things simple.

As @rindi mentioned, stick with EXT4 for all disks.

This will keep your setup very simple.

Aside: If you're really curious about pros + cons of various Linux Filesystems, open another question with a subject similar to...

Describe pros + cons of various Linux filesystems you've found in your experience.

This will likely produce a lively + useful set of comments.

Thanks for your support 

You may want to look into LVM as partitioning scheme to allow for adaption.