Look here for details. I cannot understand why.
This should have answered your question:
==> Creating zstd-compressed initcpio image: ‘/boot/initramfs-linux-cachyos-fallback.img’
cat: write error: No space left on device
It looks like you’re reusing a boot partition from another install. If so, you need to grow that partition to use the same method of install, or use manual partitioning to use a different boot partition.