Moving/migrating Kerio Connect to Nextcloud

Hey, guys. I’m looking for your knowledge and ideas regarding the following task:
I have to switch from Kerio Connect on Linux to Nextcloud in the next weeks. To complete the task I need to move several user accounts (including mail, tasks, calender and contacts) to Nextcloud.
Is there a solution to migrate/move all accounts and data to Nextcloud? Just using IMAP transfer is not enough because task, calendar and contacts are not supported.
Thank you for your help!