So i formatted the usb with EF00 as type, then mkfs.fat -F32 /dev/sdX, then zpool import rpool -R /mnt, then mounted - proc, sys, dev, run to /mnt/(respectively), then chroot into /mnt, and i ran proxmox-boot-tool format /dev/sdX, proxmox-boot-tool init /dev/sdX and proxmox-boot-tool refresh...