at https://pve.proxmox.com/wiki/Logical_Volume_Manager_(LVM) it says that i can resize the volume
# lvresize --size +<size[\M,G,T]> --poolmetadatasize +<size[\M,G]> <VG>/<LVThin_pool>
Maybe I have to do that and the this will free up space? I dont understand why the volume uses up all disk...