I did it a disservice earlier, installing the upgrade of Nextcloud to version 10.*.* doesn't actually remove the calendar and contacts apps, it just disables them re-enabling them restores them without loss of data.
Hopefully this manual upgrade is a one-off and in future the automagical system will work.
-- Phil Thane
www.pthane.co.uk phil@pthane.co.uk 01767 449759 07582 750607 Twitter @pthane