I use TrueNAS Scale as root OS and have it run a Linux VM, which is easily done via their 'Virtualization' feature. No need for Proxmox. Afaik it works a lot better to give zfs direct access to underlying hdds.
TrueNAS also has an 'Apps' feature, which are basically glorified helm chart installs on k3s that TrueNAS installs for you. But I prefer more control so I have k8s on the Linux VM. Whats also great is that the k8s on the Linux VM can use the TrueNAS storage via democratic-csi.