How to properly move data from one system to another?

I recently bought some new hardware (Processor, RAM, Drives etc…) and planning to build a NAS (using TrueNAS). ATM I have just 1 4TB drive that is being managed by OpenMediaVault (running in a VM on my Proxmox server), which has several different directories for share(s) for different VMs/Services, including Nextcloud.

I’m using Nextcloud-AIO docker container BTW.

What would be the best strategy to move my Nextcloud data consisting of 6 users from this 4TB drive to my new TrueNAS system?

This is how the directory structure looks like ATM in my OpenMediaVault server.