How to Show WordPress Recent Posts from Specific Category

First of all, install and activate the Recent Posts Widget Extended plugin on your site. It allows you to filter posts by category and tag.

After activating the plugin, click on Appearance >> Widgets and drag-drop the 'Recent Posts Extended' widget to your sidebar.

Its settings will be expanded automatically. Now select the category that you want to display in Recent Posts.

This widget comes with a lot of options (thumbnail, date, relative date, post summary settings) which you can customize as per your requirement.

After making all the settings click on the Save button. Now you can go to their website to check it.