You might have tried everything. But I have no idea what "everything" is, unfortunately for you we know exactly what you tell us. I am not even sure of the issue is an icloud mail account of a daldav connection to icloud.

Traditionally Apple make it as hard as possible to find the endpoints to use for calendars. That is not something I can address as I simply am not a customer. This information from 2013 is still being offered around the web as a method of deriving the relevant components of the endpoint URL. https://nico-beuermann.de/blogging/index.php?archives/115-English.html

This topic covers some changes for apple two factor authentication. https://askubuntu.com/questions/911567/how-to-sync-icloud-calendar

To be sure if your sunbird is using caldav, then it will have the correct endpoint. But if it is using an ICS file the best you will ever get is a read only access which is far from optimal.

Regardless, it will be Apple two factor authentication that is the issue here I would guess.

Hello Matt: Thank you for replying to a frustrated note rather than an informative one. I will try and describe what I have done and some of my thoughts on the situation. Bear in mind I am not very computer literate so some of the terms you use may be foreign to me.

Situation: I want to sync with my wife's iCloud calendar on her Mac. I do not need full sync capability, read only is fine as long as it updates any changes or additions she makes.

The approach I used I found on the web was as follows:

    - Open the calendar app on the Mac (I assumed that was to open the calendar on my wife's Mac)
    - Right-click a specific calendar (control click on the Mac)
    - Select "share calendar"
    - Click the "Public Calendar" checkbox in the dialog

The URL displayed after this last step can then be used to create an iCalendar (ICS) not CalDAV, in Thunderbird that is read only. [This is fine with me]

Going to Lightning I do the following:

    -Control click on the left panel where all the calendars are located
    - Click on “new calendar”
    -The dialog box comes up with the choices of “on my Mac” or “on the network”
    - I choose “on the network”, then continue.
    - The next dialog box that comes up offers the following:
         - Usename (unsure of what they are asking for, but put in my wife’s calendar name}
         - Location, which I fill in with the URL I got from the first set of actions.
          - Click continue and get the spinning wheel that never ends and no calendars are found.

I did this a bunch of times, using different names but none work.

I go back to Sundbird and control click the left panel and follow their instructions for “new Calendar”

    -The dialog box comes up with the choices of “on my Mac” or “on the network”
    - I choose “on the network”, then continue.
    - The next dialog box that comes up is a little different from that of Lightning as it offers a format option of
         - Calendar (ICS)
         - CalDAV
         - Sun Java

- I choose ICS - The remaining box askes for location which I fill in with the URL of my wife’s calendar - Clicking continue brings up another dialog box asking for a calendar name, color.

- Clicking continue and my wife’s calendar appears on Sunbird.

OK, this does not make any sense to me. So what are the differences between Lightning and Sunbird. I have no idea if Sunbird is using CalDAV or ICS. How would I find out?

When I set up Sunbird my home calendar was hosted on a server.

    {http://icalx.com/private/quitord/Home.ics}

When I set up Lightning I just added a calendar, which I guess is “On my mac”

Could this be the factor that is stopping my adding my wife’s calendar? BTW, other ICS calendars added such as US Holidays can be added to lightning with no issues.

Matt, sorry for the long reply. Please advise if you need additional information or want me to take different steps.

Thank you for any help you can provide.

Jim