I've heard things about TrusNAS scale, which is Debian based and should be good for running containers and/or VMs. Proxmox is a good choice for VMs, but I don't know that I'd use it for a NAS unless I'm doing controller passthrough to a VM. Proxmox does have built-in support for Gluster and ZFS, but I have never used those features (and Gluster is generally more intended for spreading a NAS across multiple servers).
I wrote a good bit on NAS options I've used in this comment on a post from a few days ago.
Best of luck in your migration/upgrade whatever option you go with.