Drupal 7 now has a "changed" property on the user entity

Drupal 7.83 includes an update which adds a "changed" field to the users table.

This means that the user entity will now have a "changed" property that reflects when the entity was most recently modified.

If needing to migrate this new value from D7 to D9, refer to https://www.drupal.org/project/drupal/issues/3252133 for further details.

The new changed attribute can be accessed as follows:

global $user;

if ($user->uid) {
  // User is logged in.
  $user_changed = $user->changed;
}