getRelatedListCount.js

import { LightningElement ,wire,api} from 'lwc';
import { getRelatedListCount } from 'lightning/uiRelatedListApi';
export default class GetRelatedListCount extends LightningElement {
    error;
    responseData;
    @api recordId;
    //Account's related contact list count
    @wire(getRelatedListCount, {
        parentRecordId: '$recordId',
        relatedListId: 'Contacts'
    })listInfo({ error, data }) {
        if (data) {
            this.responseData = data;
            //console.log('data: '+JSON.stringify(data));
            this.error = undefined;
        } else if (error) {
            this.error = error;
            this.responseData = undefined;
        }
    }
}