Proxmox or Incus can use ZFS, but i doubt you’d be able to directly move your container datasets from TrueNAS. You’d most likely have to rebuild the containers and/or move application configs/dbs. If you keep static data in datasets (your video media for instance), those will transfer over fine.

Proxmox might be overkill especially if you’re not using high availability features. I only use it on one of my machines because switching is too much hassle, but every new system I set up uses Incus on top of regular Debian.

For a big migration, you can use a cheap VPS for compute + Backblaze for a ton of cheap storage to help. For instance you could install TrueNAS on the VPS, move all your stuff over to the cloud temporarily, wipe your local hardware and install Incus, then move your containers back to your hardware. The other option is to do the opposite and set up the new environment in the cloud, then when its setup, wipe your local and move your new OS to on-prem.

But yeah this would be a time/research investment, rather than the monetary investment of just upgrading your cards.