Sure, if you have exactly one client that can access the server and you can ensure physical security of the actual network, I suppose it is fine. Still, those are some severe limitations and show how limited the ancient NFS protocol is, even in version 4.

NFS is bulletproof.

For it to be bulletproof, it would help if it came with security built in. Kerberos is a complex mess.

If someone compromises the host system you are in trouble.

Not only the host. You have to trust every client to behave, as @forbiddenlake already mentioned, NFS relies on IDs that clients can easily fake to pretend they are someone else. Without rolling out all the Kerberos stuff, there really is no security when it comes to NFS.

archival strength USB NVME drive,

Does such a thing exist? Ordinary flash storage is pretty bad at keeping its content when powered off for a long time, due to how flash memory works. I’d be curious about such drives.

Thanks, I think the risk here is that there may not be hardware to read it.

M-Disc DVDs are readable by ordinary DVD drives. So you could simply put a USB DVD drive alongside those backup M-Discs on the shelf.