Hi Balaji,
For the mentioend use-case, I would suggest the following solution
1) Define an OnSelect event handler for the DatePicker as shown below

2) Within the OnSelect event handler action flow define a logic based on the use-case
Compare the Local Variable (mapped with the Date input) date value with the current date using the IF node and execute the JS code using RunJavaScript server action (referenced from HttpRequestHandler module)

3) Used JavaScript code
"
document.querySelector('#" + DateInpt.Id + "').blur();
"
See this sample screen DatePickerJSDemo
Hope this helps you!
Kind regards,
Benjith Sam