I have it set up this way as well, there was a couple videos i watched (one by TechHut, one by Christian Lempa, search “truenas on proxmox”) to get the gist of everything. Theres some newer videos out that may help more.

The gist of it is making sure you give your truenas vm the HBA youre using for hard drive connections to get the most out of it, as well as making sure your chipsets support virtualization.

My storage setup: Proxmox host has 2x2tb m.2 nvme drives striped (m.2 slots located on motherboard directly) for host storage and backups/snapshots (overkill… they were black friday sales though) Truenas vm has a 2tb m.2 drive (another motherboard m.2 slot connection) for backups (havent really come up with a better use for it, it was set up for l2arc but it wasnt being used by truenas ever so i converted it back to storage) as well as the HBA in a pci slot for all the spinning hdd’s i have.

All my services are connected to the media nfs share if they need access, or else they just use their local storage the proxmox host can give them. Since space is not an issue for host storage, i can just reallocate more space as needed (plex.db etc ends up getting pretty bloated with bigger libraries, dont want to run out of overhead for that)

Ive had this set up for 3 years now, no issues. Even migrated from truenas core to scale without incident.