By default the WordPress "all posts" page only allows you to filter posts by dates and categories. Hence, if you want to filter your WordPress posts by tags, you will definitely not find it easy to do.
But guess what? There is a WordPress plugin that lets you filter posts by tags right in the WordPress admin panel. It also makes it very easy to filter WordPress posts by author, date range etc. It simply gives more custom filter option in list pages (posts/pages/any custom post types).
I use the plugin on my WordPress sites and I've decided to share it with you.
How To Filter WordPress Posts By Tags With WordPress Plugin
>> Sign in to your WordPress admin panel
>> Install and activate Easy Filter WordPress Plugin
>> Go to WordPress "Settings" and click on "Easy Filter"
>> Enable "Custom Filter"; enable "Taxonomy" option and select "Tags" as seen in the screenshot below :
>> Click "Save Changes"
If you go to the "All Posts" page, you should now see the "Tags" filter option as seen in the screenshot below:
>> Click the "view all tags" dropdown, select the tag you want to display it's posts and click the "filter" button.
I hope it works for you.