Contextual hook_contextual_links_plugins_alter doesn't work

Drupal version 9.0

I'm trying to implement hook_contextual_links_plugins_alter (or hook_contextual_links_alter) in a theme. My theme is called basic_theme and the function is declared inside basic_theme.theme

function basic_theme_contextual_links_plugins_alter(array &$contextual_links) {
  // ...
}

function basic_theme_contextual_links_alter(array &$links, $group, array $route_parameters) {
  // ...
}

It doesn't work. Does this hook work inside a theme?
Thanks for the help