The new default systemd-boot (managed via sdbootutil) instantly fills up the tiny EFI system partition (ESP) on a Chromebook. This happens because it copies multiple large kernel images and initrd files directly into the limited EFI space.
The only reliable method for a successful installation is to manually switch the bootloader to GRUB2-EFI in the final installation summary screen of the openSUSE installer before committing the changes.