Mail app -> Calendar app integration: how does it work?

The description in the app store says,

Integration with other Nextcloud apps! Currently Contacts, Calendar & Files – more to come.

When I get an email with an ICS as an attachment, my only options are to download it or store it in files. Is there a way to integrate mail with calendar so that the calendar gets updated when I receive an invitation?

You can import ICS if they have the correct MIME set by the server. If you can only download then the MIME is most likely wrong.

I have the same problem. Which server are you referring to that needs to set the correct MIME? The email server of the individual that sent the calendar invite or the email server that receives my email (and that i use by IMAP in the nextcloud mail app)?