@shirishag75 Depending on what app/interface you use, there should be a post visibility setting when you write a post. It may look like a globe/earth icon, just switch it to a different one like unlisted, followers-only or direct.
This is what it looks like in Tusky:
@shirishag75 You should be able to do that by just clicking on the globe icon, not sure what is your issue 🤔
I checked in my Firefox, also on Debian Testing etc. There is the same button as in Tusky for setting post visibility, as shown above.
You can just write a toot (tweet) including @unicorn and set post visibility to direct, then only I can see it.
You can also do this for several people by just mentioning them all in the toot.
So if I just post a toot with @shirishag75 and set it to "direct" then only you can see it :)