Google is testing an update for the Play Store in which it is removing the Installed and Library tabs from the 'My apps & games' section to give it a cleaner look. The Installed tab on the Play Store contains a list of all the applications installed on your current Android device, while the Library contains a list of all the apps and games you have ever installed across all your Android devices linked to your Google account.
The latter is particularly useful since it can help you find apps and games that you had installed long ago on your previous Android devices but were struggling to recall their name. However, it looks like these two tabs were not being used much by users which is perhaps why Google is removing it in favor of a cleaner look.
It is unclear how Google will allow users to view their previously installed set of apps on the Play Store if the Library section is removed.
Google is rolling out this change as a server-side update, though it is unclear if this is a part of A/B testing by the company or not. Just recently, Google had rolled out an update for the Play Store to show the download count, size, and ratings in the search results.