Let's imagine we don't want to have any restrictions for our route. For this we can set _access requirement to TRUE.

your_module.route_name:
  path: '/your_path'
  defaults:
     _controller: 'Drupal\your_module\Controller\YourController::yourMethod'
  requirements:
    _access: 'TRUE'

If you have a basic path we can get route using router.no_access_checks service. Keep in my you have to have a leading slash

$router = \Drupal::service('router.no_access_checks');
$result = $router->match('/node/2');

In case you have URL object we can get route from it like this

$router = \Drupal::service('router.no_access_checks');
$result = $router->match($url->toString());

To get route by name in Drupal 9 we need to use router.route_provider service.

$route_provider = \Drupal::service('router.route_provider');
$route = $route_provider->getRouteByName('user.page');

To check this we need to use router.admin_context service

if (\Drupal::service('router.admin_context')->isAdminRoute()) {
   // Do something here.
}

We also can check a specific route

$route_provider = \Drupal::service('router.route_provider');
$route = $route_provider->getRouteByName('user.page');
if (\Drupal::service('router.admin_context')->isAdminRoute($route)) {
   // Do something here.
}