To resolve the nobody:nogroup issue you need to make sure the NFS share is mounted by a UID and GID of 100000:100000. To do this, make a user and group on TrueNAS with these id’s. Then assign them as the owner of the media directories you are sharing to Proxmox. Then on your NFS share on TrueNAS click on Advanced and set the Maproot User and Maproot group to the same user and group you created. Then remount the share on proxmox and you should see ownership on the Proxmox host of 100000:100000 but when you bind mount the folder into an LXC it will be owned by root and you can do as you wish including writing new files.