Yes, you can use both disks as JBOD (just a bunch of disks) or RAID0, but you will never get the full 36 GB anyway, because it should be more like 35 plus/minus. But: if you set up a NAS like this as RAID0, if one disk fails, all the data is lost. I recommend a NAS, because you can work with smaller disks and a NAS will cost less in the long run, because the question is not if the disks will fail, only when. They will all fail, sooner or later, and a NAS with hardware failure protection and RAID5 is much cheaper. And I also recommend a NAS that gets much more support. This one is much more powerful (4 core and 4GB RAM, expandable, can also run virtual machines, you can also install additional programmes):

Synology DS920+ (0 TB)

Plus 4 x 12 TB Seagate Ironwolf:

Seagate IronWolf (12 TB, 3.5", CMR)

This solution is a bit more expensive, but it gives you 36 TB of storage and if one disk fails, you only need to buy a 12 TB disk as a replacement, which is cheaper than an 18 TB disk. Later expansion to double the storage capacity would also be possible, because by replacing each 12 TB disc with a larger one, you can expand the capacity without disconnecting the NAS from the network.