How to make user.html.twig template for two different pages (users)?
Platon, you appear to be mixing up the template for the user itself (user.html.twig) and the overall page template (page.html.twig).

If you want to override the user template then you need to implement hook_theme_suggestions_HOOK where "HOOK" is "user" which is the theme hook you are overriding.

Here is an example of what that code would look like if you were using Bartik (but of course in practice you should be using your own subtheme rather than hacking core):

function bartik_theme_suggestions_user_alter(array &amp;$suggestions, array $variables) {
  $suggestions[] =  'user__' . $variables['elements']['#user']-&gt;id();
  return $suggestions;
}