Does deleting user account on macOS also deletes their installed apps?
On macOS, an app bundle (.app file) can technically be located anywhere. Although, in the most general case, apps are installed in the shared /Applications directory and in some cases in the directory with same name in the users Home directory ~/Applications (or more completely /Users/&lt;username&gt;/Applications).

Deleting a user account deletes the users Home directory. Thus, all the app installed by user in the root /Applications directory remain unaffected.

Usually, when deleting a user account, macOS gives an option to preserve their Home directory contents. Any app installed in the Home directory can technically be carried over and used.

In short, to put it simply, since users files are hidden from each other, if you were able to use an app installed by other user, you will continue to have access to it even after their account is deleted from macOS.