Based on the excellent script of wofferl.

Note: Starting from version 4.0, Proxmox Backup Server requires Debian 13 (Trixie) or distributions based on it.

1. Update the apt package index and install packages to allow apt to use a repository over HTTPS:

   sudo apt update
   sudo apt install -y ca-certificates curl gnupg lsb-release

2. Add GPG key:

   mkdir -p /etc/apt/keyrings
   sudo curl -fsSL https://dexogen.github.io/pipbs/gpg.key | sudo gpg --dearmor -o /etc/apt/keyrings/pipbs.gpg

3. Use the following command to set up the repository:

   echo "deb [arch=arm64 signed-by=/etc/apt/keyrings/pipbs.gpg] https://dexogen.github.io/pipbs/ trixie main" | sudo tee /etc/apt/sources.list.d/pipbs.list

1. Update the apt package index:

   sudo apt update

2. Install packages:

   sudo apt install -y raspberrypi-kernel-headers pv zfs-initramfs zfsutils-linux
   sudo apt install -y proxmox-backup-server

If you encounter issues, first check the Help section and consult the official Proxmox Backup Server documentation.