[SalesForce] Error while inserting contentdocumentlink with Collaborator access through Apex

while researching a problem similar to yours, I found an answer you might find useful:

Document already Linked

Basically the idea is to introduce a check on whether there is an existing ContentDocumentLink with the same LinkedEntityId before inserting. However, the check avoids the error but prevents insertion, which is after all not that different from your try / catch block. I still haven't found a solution to avoid the error AND insert the record. I'll keep you posted if I find it.

You need to put a check to verify if ContentDocumentLink records exist before putting it into final list ContentDocumentList. Logic will be like this.

trigger ContentVersionTrigger on ContentVersion (after insert) {
    if(!TriggerRunOnce.hasAlreadyfired())
    {
        List<user> users = [select user.id, user.Email, user.FirstName, user.LastName, user.profile.name, user.Username, user.IsActive 
        FROM user, user.profile 
        where user.LastName IN ('***','***') and user.IsActive=true];
        Set<Id> contentDocumentIdSet = new Set<Id>();

        for(ContentVersion cv:trigger.new)
        {
            if(cv.ContentDocumentId != null)
            {
                contentDocumentIdSet.add(cv.ContentDocumentId);
            }
        }

        List<ContentDocumentLink> lstContentDocumentlink = [SELECT ContentDocumentId, LINKEDENTITYID 
                                                            FROM ContentDocumentLink WHERE ContentDocumentId IN:contentDocumentIdSet];


        List<ContentDocumentLink> ContentDocumentList = new List<ContentDocumentLink>();


        for(ContentVersion cv:trigger.new)
        {
            system.debug('at 5 '+cv);
            if(cv.ContentDocumentId != null && !lstContentDocumentlink.contains(cv.ContentDocumentId))
            {
                for(user u:users){
                    if(u.Id != cv.OwnerId){
                        ContentDocumentLink cdl = new ContentDocumentLink(ContentDocumentId=cv.ContentDocumentId,LINKEDENTITYID = u.Id,SHARETYPE='C');
                        ContentDocumentList.add(cdl);  
                    }
                }
            }
        }

        insert ContentDocumentList;
        TriggerRunOnce.setAlreadyfired();
    }
}