Problem with storage local

I think you select the wrong storage. Check your storages, one is for PVE / ISO and the other one might be an LVM Thin. You should move your virtual disk to the other storage.
 
Take a look at the disks with fdisk to check if you have unused space / partition and check mount if they is already mounted and ready to use.
 
Nobody what?

Like @sb-jw wrote in #4, what about fdisk and mount?

And like @sb-jw wrote in #2, if you have 2 Terabyte disk but use only 200 G, there is unused space that can be mounted and added as storage to Promox. It's in Server | Storage | Add and choose Directory in this case.