Enable email invitations for CalDAV servers

Hi there,

I use a radicale CalDAV server to synchronize my calendars between my devices, which works fine so far.

But when I add some participants, Thunderbird will not send out any invitations. radicale has no such feature, thus Thunderbird should take care of this. This article at the knowledge base (KB) describes exactly what I want to achieve. However, the Prefer client-side email scheduling option is greyed out (cannot be activated). Sure enough, I have assigned an email account to the calendar.

The KB article states:

This option will be only visible for CalDAV calendars but not for any other type of calendar

Since this is a CalDAV calendar I do not understand, why the option is greyed out. For CalDAV calendars hosted on NextCloud servers, the option can be activated. IMHO this option should be available for all CalDAV calendars, like described at the KB article.

Or am I doing something wrong here?