Post Chatter with multipe User names to address

Trigger Handler Class & Trigger on After Update:

 private void postChatterupdatecase(ClsWrappers.TriggerContext trgCtx) {
        if (trgCtx.isAfter && trgCtx.isUpdate){
            Set<Id> ownerManagerIdSet = new Set<Id>();
            Map<Id,Case> oldCaseMap = new Map<Id,Case>();
            for(sobject so : trgCtx.oldList){
                Case csOld = (Case)so;
                oldCaseMap.put(csOld.Id,csOld);
            }
            for(sobject so : trgCtx.newList){
                Case cs = (Case)so;
                ownerManagerIdSet.add(cs.OwnerId);
            }
           
            Map<id,User> user_map = new Map<id, User>(
                [select Id,isActive,manager.Id from User where isActive = true AND Id IN: ownerManagerIdSet LIMIT 5000]);
            System.debug('*********** user_map *' + user_map);
            for(sobject so : trgCtx.newList){
                Case cs = (Case)so;
                if (cs.Milestone_message__c != oldCaseMap.get(cs.Id).Milestone_message__c && user_map.containsKey(cs.Ownerid)){
                    if(cs.Is_Violation_Action__c == true && cs.Milestone_message__c != null){
                        if(user_map.get(cs.OwnerId).manager.Id != null){
                            CreateChatterFeed.ChatterAPI(cs.Milestone_message__c,  new List<Id> {user_map.get(cs.OwnerId).manager.Id, cs.OwnerId}, cs.Id);
                          // cs.Milestone_message__c = null;
                        }
                        else{
                            CreateChatterFeed.ChatterAPI(cs.Milestone_message__c, new List<Id> {cs.OwnerId}, cs.Id);  
                        }
                    }
                    if(cs.Is_Violation_Action__c == false && cs.Milestone_message__c != null){
                        CreateChatterFeed.ChatterAPI(cs.Milestone_message__c, new List<Id> {cs.OwnerId}, cs.Id);    
                    }
                }
            }
        }
    }

// Chatter posting API

public without sharing class CreateChatterFeed {
    public static void ChatterAPI(String messageToPost, List<id> usersToPost, id objectToPost){
        ConnectApi.FeedItemInput feedItemInput_1 = new ConnectApi.FeedItemInput();
    String delimitor = ', ';
        ConnectApi.MessageBodyInput messageBodyInput_1 = new ConnectApi.MessageBodyInput();
        ConnectApi.TextSegmentInput textSegmentInput_1 = new ConnectApi.TextSegmentInput();
    ConnectApi.TextSegmentInput delimitorInput = new ConnectApi.TextSegmentInput();
    delimitorInput.text = delimitor;
        messageBodyInput_1.messageSegments = new List<ConnectApi.MessageSegmentInput>();
       
        for (id userToMention : usersToPost){
      ConnectApi.MentionSegmentInput mentionSegmentInput = new ConnectApi.MentionSegmentInput();
            mentionSegmentInput.id = userToMention;
            messageBodyInput_1.messageSegments.add(mentionSegmentInput);
            messageBodyInput_1.messageSegments.add(delimitorInput);
        }

           
        textSegmentInput_1.text = messageToPost;
        messageBodyInput_1.messageSegments.add(textSegmentInput_1);
        feedItemInput_1.body = messageBodyInput_1;
        feedItemInput_1.feedElementType = ConnectApi.FeedElementType.FeedItem;
        feedItemInput_1.subjectId = objectToPost;
        if(!Test.isRunningTest()){
            ConnectApi.FeedElement feedElement = ConnectApi.ChatterFeeds.postFeedElement(Network.getNetworkId(), feedItemInput_1);
        }
    }
}

Output: