Updating event via MS Graph API removing Join Button in the event

I have created an event in the outlook calendar. The event contains Teams join link. While I am updating the event from MS Graph API, the join button is being removed.

Here is the sample code of what I am doing:

void UpdateEventInCalendar(string eventId)
{
    var getCalEvent = Task.Run(() =>
            {
                return service.Me.Events[eventId].Request().GetAsync();
            });
    Task.WaitAll(getCalEvent);
    BodyType bodyType = BodyType.Text;
    Event eventToUpdate = getCalEvent.Result;
    Event updatedEvent = new Event();
    updatedEvent.Id = eventToUpdate.Id;
    updatedEvent.Subject = "Updated text";
    updatedEvent.ShowAs = eventToUpdate.ShowAs;
    updatedEvent.Body = new ItemBody
            {
                ContentType = bodyType,
                Content = "Some new content"
            };
    graphServiceClient.Me.Events[updatedEvent.Id].Request().UpdateAsync(updatedEvent.Id);
}

Event before update:

Event update content:

Event after update:

How to keep the event while updating the event?

As a workaround you can try this to keep your online meeting appeared:

First: in your addEvent function, your body should be like this

AddedEvent.Body = new ItemBody
            {
                ContentType = BodyType.Html,
                Content = "<p id = 'MsgContent'>Your Body</p>"
            };

Second: In the update event, you can change the body content like this

                HtmlDocument html = new HtmlDocument();
                html.LoadHtml(EventToUpdate.Body.Content);
                html.GetElementbyId("Msgcontent").InnerHtml = "Your new body";
                updatedEvent.Body = EventToUpdate.Body;
                updatedEvent.Body.Content = html.DocumentNode.OuterHtml;