And thanks for the instructions. I've been running this docker with Valheim since Feb 4th, and it's been very stable. Here is my user script to backup World files; I have mine set to run at 03:30 daily. Note that your destination paths will be different, so make sure you update it to match your setup.
#!/bin/bash
# Create a compressed file archive as a backup for the Valheim server
today=$(date '+%m_%d_%Y__%H_%M_%S')
backup_path=/mnt/user/CA-backups/valheim_backup
source_path=/mnt/user/appdata/valheim/.config/.
backup_file=$backup_path/valheim_$today.7z
7z a -t7z -m0=lzma -mx=9 -mfb=64 -md=32m -ms=off $backup_file $source_path
# Keep only the 10 newest backups
ls -t $backup_path/*.7z | awk 'NR>10' | xargs --no-run-if-empty rm -f