It may help if we could see your Photoshop System Info. Launch Photoshop, and select Help > System Info... and copy/paste the text in a reply.
Hey Jeffery
Thanks for your kind interest and prompt reply, but it appears that i was able to solve the problem and finally got the Select Subject option in my Photoshop CC 2018. The fix was relatively simple for me, i just uninstalled the application and this time at the time of uninstall through creative cloud, i removed all the app preferences unlike the previous attempt wherein i had kept my app preferences, after the uninstall, when i reinstalled the application, it worked totally fine with the missing Select Subject option now visible from both the selection tools and the select dropdown menu.
I hope this thread and this solution will help any other people facing a similar issue.
Many thanks to c.pfaffenbichler too for his efforts to help me solve the issue!
You guys are great!!