How to combine all HDD Available and Used Storage in Linux (Print Only)

I want to merge my all drives total available storage nad used storage.When i use lsblk i get this result

NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
nvme1n1 259:0 0 1.8T 0 disk
├─nvme1n1p1 259:2 0 4G 0 part [SWAP]
├─nvme1n1p2 259:3 0 1G 0 part /boot
└─nvme1n1p3 259:4 0 1.8T 0 part /
nvme0n1 259:1 0 1.8T 0 disk /home2

So i want to merge all nvme1n1 and nvme0n1 so when i try to modifylsblk -b --output SIZE -n -d

I get this result
1920383410176
1920383410176

But the problem is i want to merge all blocks available and show total in GB4000 GB

Additional requirement is i wasl want to show total all used blocks on all hdd in GB.

Can anyone help please?