JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://code.jquery.com/jquery-3.6.1.slim.min.js"></script>

JavaScript

;let recipients = [
{"id":"666777","lawfulBasis":"0","jurisdiction":"AMER","name":"David G"},
{"id":"888999","lawfulBasis":"1","jurisdiction":"ASIA","name":"Mike A"},
{"id":"444555","lawfulBasis":"2","jurisdiction":"EUR","name":"John No Sub"}
];

let serviceSubscriptions =  [
{"recipientId":"666777","serviceId":"3218143"},
{"recipientId":"666777","serviceId":"8956799"},
{"recipientId":"888999","serviceId":"15656200"},
{"recipientId":"000000","serviceId":"3721"}
];




const recipientObj = recipients.map(({id,isSubscribed,...recipient}) => {
  //if (isSubscribed === true) {
      return {
      		id,
          isSubscribed: serviceSubscriptions.some(( subs ) => subs.recipientId ===id),      	
          test:'test',
          services: serviceSubscriptions.map(({recipientId,serviceId}) => serviceId+':'+serviceSubscriptions.some(({serviceId}) => recipientId === id)),
          servicesExample2: '3218143,3218143',
          
          servicesDEV:,
          
          ...recipient,
          
        }
    //}
});

console.log(recipientObj)





/*
const testArr = [
  ...serviceSubscriptions
    .reduce((acc, { recipientId, serviceId }) =>
      acc.set(recipientId,
        (acc.get(recipientId) ?? new Set).add(serviceId)), new Map)
    .entries()
  ]
  .map(([recipientId, serviceIds]) => ({
    recipientId,
    services: [...serviceIds].join(',')
  }));

//console.log(testArr);
console.log( ...serviceSubscriptions).reduce

*/