How can I get flag count of a flag? I see extensive Drupal 7 documentation for the Flags module, but very little for Drupal 8. 
I have a Signup flag on a Drupal 8 node (which is an event). I need to suppress the Signup link when a number of signups (flags) have been added to this node.

I'm trying with hook_preprocess_flag() using the following code.

$flag_service = \Drupal::service('flag');
$flag = $flag_service-&gt;getFlagById('signup');


What call gets the flag_count of that flag?
For flag count on entities use: 

$flag_service = Drupal::service('flag.count');
$counts = $flag_service-&gt;getEntityFlagCounts($node);


For flag count on flag entity use:

$flag_service-&gt;getFlagFlaggingCount($flag);


You can find all functions from the Service here:

/modules/contrib/flag/src/FlagCountManager.php