Sync custom calendar activity with other email services in NodeJS

Right now, I am designing a custom react calendar, with NestJS as backend support and what I am trying to achieve is to sync my calendar with other online calendar service like google calendar, outlook, zoho calendar, iCalendar or any other calendar service.

Right now I am looking at calDAV service and from what I gathered, I only found the calDAV api for google (which I am yet to implement) but I'm not understanding how I can integrate other email services as well.

It would be really helpful if the community can guide me on my track on which and how to use calDAV or any other services which can be helpful in my case.