I am trying to display opportunity share records in lwc data table, I am getting blank rows even though when i execute the query in the workbench, records are being returned with values.

Code below:

    import {LightningElement, track, wire} from 'lwc';
    import getOppdata from '@salesforce/apex/LWCExampleController.retriveOpportunities';
    const columns = [
        {
            label: 'User',
            fieldName: 'UserOrGroupName',
            type: 'text',
        },
         {
            label: 'AccessLevel',
            fieldName: 'OpportunityAccessLevel',
            type: 'text'
        }
    ]
    export default class OpptyAccountLWC extends LightningElement {
        @track data = [];
        @track columns = columns;
    
        @wire(getOppdata)
        opp({error, data}) {
            if(data) {
    
                let currentData = [];
    
                data.forEach((row) => {
    
                    let rowData = {};
    
                    rowData.User = row.UserOrGroup.Name;
                    rowData.AccessLevel = row.OpportunityAccessLevel;
                    //window.alert('########## '+row.UserOrGroup.Name );
                    //console.log('########### '+ row.UserOrGroup.Name);
    
                    currentData.push(rowData);
                });
    
                this.data = currentData;
            }
            else if(error) {
                window.console.log(error);
            }
        }
    }

HTML:

    <template>
        <lightning-card title="OpptyShareRecords">
            <lightning-datatable columns={columns} 
                                data={data} 
                                key-field="id"
                                hide-checkbox-column="true"
                                show-row-number-column="true"></lightning-datatable>
        </lightning-card>
    </template>

Controller class:

    public class LWCExampleController {    
        @AuraEnabled(cacheable=true)
        public static list<OpportunityShare> retriveOpportunities() {
            return [SELECT OpportunityAccessLevel,UserOrGroup.Name
                    FROM OpportunityShare];
        }
    }