yes you are missing something. Right click the calendar in the calendar list. Properties will show an email address. Use the drop down list to change it and incoming mail to that address will automatically be included in that calendar.

Each calendar can only have one email address, but none is an option and it is then that you are asked IIRC. I have not really looked at the calendar for more than a decade. I use my phone when a calendar is needed.

Thanks for the hint, That moved my problem one step further.

Changed the Email under "calendar" to my Gmail. But the "URL place" needs to updated. It's is showing the one to, in this case "one.com", where my privite Email is registered. But in this case I need to be the Gmail "caldav..." URL. But it cannot be altered in the setting window.(Called "place in Swedish.) As you can see in the attachement I also have a calendar called kagerja@gmail.com. But I can´t link any incomming invitations to it from other persons. Only I I send my self an invitation from private Email.

See attached file