Status of task synchronization in Roundcube

I’ve been trying to sync tasks in Roundcube with Thunderbird for some time now.  It started with tasks not being enabled by my ISP, which I got them to enable.  Then I would have fleeting success adding a calendar with task support in Thunderbird only for it to give me “Please select a calendar that supports tasks” after a short time with no correlation to anything I did, apparently.  When I added calendars via the Calendars and Contacts Management page at

/frontend/jupiter/calendar-contact-management/index.html#/list

they would appear in Roundcube, but I wouldn’t be able to save any tasks or events.  When I try to create a calendar in Roundcube it takes me to the same page, namely

/webmail/jupiter/calendar-contact-management/index.html#/list

where I can create a “collection”, although I have no direct way of figuring out what its URL is.  When I try to sync to it from Thunderbird using

https://mail.mydomain.com:2080/calendar/myaddress@mydomain.com/calendar

I can find and sync to the calendar just fine.  Most importantly I can add events and tasks, but this appears to contradict this link

https://support.cpanel.net/hc/en-us/articles/27989202528535-CalDAV-calendars-cannot-be-added-in-Roundcube

or would that be another procedure?  The bottom line is I can’t sync tasks between Roundcube and Thunderbird no matter how I try.  Is there any workaround for this?  If not, will this ever be possible in the foreseeable future?