Proxmox change from local-lvm to local storage

First remove the existing LVM-Thin:

lvremove pve/data

Then create an normal lvm on existing group. For example:

lvcreate -L 755.96G -n data pve

Format it:

mkfs.ext4 /dev/pve/data

Mount it in the fstab. The mount target must be empty, so delete everything in there.

/dev/pve/data /var/lib/vz ext4 defaults 0 2
rm -rf /var/lib/vz/* && mount -a

After all create you normal directory storage.