Chatter Api Access to create Feed via Platform Trigger

I am trying to Create A chatter feed using Chatter API(As I need mention user in the post) from A platform event trigger. But I am getting an error:- "Insufficient Privileges: The Connect API is not enabled for this user type." in Debug Logs

and the user that's shown on debug log is Automated Process and not the Authenticated user creating a post request.

So my question is Do I need to Authenticate to Chatter API inside the trigger? If yes How I can do that.

Or am I missing any chatter Configuration?

Trigger Code

trigger SampleEventsTrigger on Sample_Events__e (after insert) {
System.debug('Event Log');

for (Sample_Events__e event : Trigger.New) {
    System.debug('Event: ' + event);
    //postFeedForSmartwinnr.PostFeedMethod(event.CreatedById, event.userId__c, event.Notification_message__c); // Call function to Create Chatter
    ConnectApi.FeedItemInput feedItemInput = new ConnectApi.FeedItemInput();
    ConnectApi.MentionSegmentInput mentionSegmentInput = new ConnectApi.MentionSegmentInput();
    ConnectApi.MessageBodyInput messageBodyInput = new ConnectApi.MessageBodyInput();
    ConnectApi.TextSegmentInput textSegmentInput = new ConnectApi.TextSegmentInput();
    System.debug('feedItemInput: ' );
    System.debug(feedItemInput);
    messageBodyInput.messageSegments = new List<ConnectApi.MessageSegmentInput>();

    mentionSegmentInput.id = event.userId__c;
    messageBodyInput.messageSegments.add(mentionSegmentInput);

    textSegmentInput.text = event.Notification_message__c;
    messageBodyInput.messageSegments.add(textSegmentInput);
    System.debug(feedItemInput);
    feedItemInput.body = messageBodyInput;
    feedItemInput.feedElementType = ConnectApi.FeedElementType.FeedItem;
    //feedItemInput.subjectId = '0F9RR0000004CPw';
    System.debug(feedItemInput);
    ConnectApi.FeedElement feedElement = ConnectApi.ChatterFeeds.postFeedElement( Network.getNetworkId(), feedItemInput); // Error is on this line 
    System.debug('feedElement');
    System.debug(feedElement);
    }
}

Thanks in Advance...

As per my knowledge, the user present at that point is Automated Process who is able to post feed using class but, don't have access to chatter REST API