Thanks for the Help. You are brilliant. That fixed my problem and now i can use my Nextcloud via https and without security issue.
For the other questions:
I used this command from an other Thread.
https://help.nextcloud.com/t/help-me-to-enable-hsts-http-strict-transport-security-on-my-nc22-instance-please/121552/8?u=lightningstorch
For the mounted Volumes:
The Truenas App Folder is on a NVME ssd without mirror and the Volume for the Data is on my 8 TB Mirrored HDD Storage.
I changed the Settings in Truenas by the installation to the correct Folder on the seperate Storage.