Meta key filters let you filter the posts based on the Selected Meta key or Post Meta key.
Select Meta Key
In the Select Meta key type filter, you can easily include the desired meta keys and exclude the meta keys based on requirements.
Post Meta Key
In Post Meta Key, you can return the results based on the value comparison for the post meta key.
For example, if you have a custom field of type "text" assigned to posts and valued it with "1" in one of your posts. Then with the below filter, only that post will return in the grid.
There are, however, many other operators in the dropdown that you can make use of.