I have the same issue in a similiar situation and I like to give some additional information on my environment.
Non privileged Debian (Bookworm) LXC with Rootdisk on a ZFS drive. Latest docker, docker-compose and portainer running. Several Docker Container running without any issues.
I then created a stack for Paperless NGX and the first installation was fine, but I had some minor issues with files outside the container.
So I stopped the stack, deleted volumes, images and containers and made my changes to the stack. After Deploying the stack I had the same issue as reported in post1. Even stopping the LXC and restore it from a backup never let me deploying the stack again. Watchtower did update other dockerfiles fine, though.
I then set up a new LXC and this time the root-fs is on a thin-lvm (ext4, nvme drive). Docker, docker-compose, portainer, Debian-version are all identical to original LXC. Anyhow this time I have been able to create and deploy the stack without any issues.
Next step: Use Backup of original LXC (ZFS), restore to LVM and redeploy stack. There might be somesthing strange with docker and ZFS. I understand Posts #15 to #19 are pointing in that direction as well, allthough Docker says the issue is fixed.
Btw. I am on Proxmox 8.0.4, but obviously the ZFS has been setup under Proxmox 6.xxx.