Apex sharing: INVALID_FIELD_FOR_INSERT_UPDATE, Visibility InternalUsers is not permitted for this linked record

I am working on a trigger helper whose requirements are:

1. If a file is shared to certain custom objects that are descendants of the Account, share that file to the Account as well
2. Based on the value of a Document Type field on ContentVersion, make that Account share visible or not visible to external partner users

When a file is uploaded by a Partner User without a qualifying document type, I get the below error. Uploading a qualifying file internally does not give the same error.

ContentDocumentLinkTrigger: execution of AfterInsert caused by: System.DmlException: Upsert failed. First exception on row 0; first error: INVALID_FIELD_FOR_INSERT_UPDATE, Visibility InternalUsers is not permitted for this linked record.: [Visibility] Class.CoachPortalDocumentShareTriggerHelper.DocumentShare: line 62, column 1 Trigger.ContentDocumentLinkTrigger: line 15, column 1

I have tried 'upsert as system' but get the same error. Using different ShareType values just causes other errors.

    public without sharing class CoachPortalDocumentShareTriggerHelper {
    // test classes in EngagementReportDisplayAndPDF_Test
    public static void DocumentShare(set<id> CDids){
        map<string,string> prefixObjectMap = getPrefixObjectMap();
        list<string> docTypesToShare = new list<string>{'Annual Reflection','Action Plan','Application','ICAT Data','ICAT Report','President\'s Letter','Engagement Agenda','Engagement Report','Opportunity Assessment','Landscape Analysis','Policy Audit','Communication Audit'};
        list<contentdocument> CDs = [select id, (select id, linkedentityid from contentdocumentlinks), (select id, ICType__c from ContentVersions where IsLatest = true) from contentdocument where id in :CDids];
        list<contentdocumentlink> upsertCDLs = new list<contentdocumentlink>();
        for(contentdocument CD: CDs){
            contentdocumentlink accCDL = new contentdocumentlink();
            contentdocumentlink otherCDL = new contentdocumentlink();
            for(contentdocumentlink CDL: CD.contentdocumentlinks){
                string linkedPrefix = string.valueof(CDL.linkedentityid).left(3);
                if(linkedPrefix == '001'){
                    accCDL = CDL;
                } else if (prefixObjectMap.containskey(linkedPrefix)){
                    otherCDL = CDL;
                } 
            }
            if(accCDL.id != null || otherCDL.id != null){
                if(accCDL.id == null ){
                    //find linked entity id
                    string objectname = prefixObjectMap.get(string.valueof(otherCDL.linkedentityid).left(3));
                    system.debug(objectname);
                    //create account CDL 
                    string accountid = '';
                    switch on objectname {
                        when 'Engagement_Report__c' {
                            accountid = [select College__c from engagement_report__c where id = :otherCDL.linkedentityid].College__c;
                        }                        
                        when 'Initiative_Participation__c' {    
                            accountid = [select participating_institution__c  from Initiative_Participation__c where id = :otherCDL.linkedentityid].participating_institution__c;
                        }
                        when 'Participant_Submission_Assignment__c' {
                            accountid = [select Program_Participation__r.participating_institution__c from Participant_Submission_Assignment__c where id = :otherCDL.linkedentityid].Program_Participation__r.participating_institution__c;
                        }
                    }
                    accCDL.LinkedEntityId = accountid;
                    accCDL.ContentDocumentId = CD.id;
                }
                if(docTypesToShare.contains(CD.ContentVersions[0].ICType__c) && accCDL != null){
                    accCDL.ShareType = 'I';
                    accCDL.Visibility = 'AllUsers';
                    upsertCDLs.add(accCDL);
                } else if (accCDL != null) {
                    accCDL.ShareType = 'I';
                    accCDL.Visibility = 'InternalUsers';
                    upsertCDLs.add(accCDL);
                }
            }
        }
        if(upsertCDLs.size()>0){
            upsert upsertCDLs;
        }
    }
    public static map<string,string> getPrefixObjectMap(){
        map<string,string> prefixObjectMap = new map<string,string>();
        list<string> objectsOfInterest = new list<string>{'Account','Engagement_Report__c','Participant_Submission_Assignment__c','Initiative_Participation__c'};
        for(string OoI: objectsOfInterest){
            DescribeSObjectResult objResult = Schema.getGlobalDescribe().get(OoI).getDescribe();
            String objPrefix = objResult.getKeyPrefix();
            prefixObjectMap.put(objPrefix,OoI);
        }
        return prefixObjectMap;
    }
}

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