You started with the statement that you installed Leap 15.2 using ESP on RAID1. This works only if openSUSE is configured for secure boot, i.e. it is using shim as primary bootloader. And in this case update-bootloader works because it calls shim-install.
If update-bootloader fails now it means it calls grub2-install directly which means you changed bootloader configuration. Show your /etc/sysconfig/bootloader and /etc/default/grub.