Hi, @Mohammad Qasim ,
I assume that if you select an item, the list & item menu or we call it ribbon shall appear. It is mostly because there are other web parts in this page. You can check it by editing the page. If there are unneeded web part, you can remove it to make the list and item ribbon get displayed all the time. And you can contact your IT if you are not sure the web part is needed or not.
Here is a .gif for demonstration.
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