You need to adjust where the contextual filter is retrieving the UID from. For your case, you want Raw value from URL with a Path Component of 2 (i.e. the UID from /user/XXX profile page).

You need to adjust where the contextual filter is retrieving the UID from.

When you provide a value for your contextual filter, you want to retrieve the raw UID value that's coming from Drupal's path system. To do this, look at the When the Filter Value is not available section.

Selecting Raw value from URL will use Drupal's internal path for the currently viewed page (e.g. /node/XXX, /user/YYY, etc.). The path component refers to which one of the "subdirectories" in the path to reference (e.g. 1 = "user", 2 = YYY, in the previous example).

In your example, you want a Path Component of 2 (i.e. the UID from /user/XXX profile page).