Thanks, i used this now. And it built,

nvme1n1         259:1    0   1.8T  0 disk  
├─nvme1n1p1     259:2    0     2G  0 part  /mnt/boot
└─nvme1n1p2     259:3    0   1.8T  0 part  
  └─enc         254:3    0   1.8T  0 crypt 
    ├─pool-swap 254:4    0    98G  0 lvm   [SWAP]
    └─pool-root 254:5    0   1.7T  0 lvm   /mnt/var/log
                                           /mnt/persist
                                           /mnt/nix
                                           /mnt

~```

          luks = {
            size = "100%";
            content.type = "luks";
            content.name = "system";
            content.settings.allowDiscards = true;

            # use a fido2 key for unlocking
            content.enrollFido2 = true;

            # do not generate a recovery passphrase
            content.enrollRecovery = false;

            content.content = {
              type = "btrfs";
              ...
            };              

this did not work,

          luks = {
            size = "100%";
            content = {
              type = "luks";
              name = "enc";
              enrollFido2 = true;
              settings = {
                allowDiscards = true;
              };
              content = {
                type = "lvm_pv";
                vg = "pool";
              };
            };
          };