Comment # 11 on bug 1101747 from Felix Miata

zypper -v in -f grub2 grub2-i386-pc grub2-x86_64-efi solved the problem, at
least for now, using this /etc/default/grub:

# If you change this file, run 'grub2-mkconfig -o /boot/grub2/grub.cfg'
afterwards to update
# /boot/grub2/grub.cfg.

# Uncomment to set your own custom distributor. If you leave it unset or empty,
the default
# policy is to determine the value from /etc/os-release
GRUB_DISTRIBUTOR="opensusetw"
GRUB_DEFAULT=saved
GRUB_HIDDEN_TIMEOUT=0
GRUB_HIDDEN_TIMEOUT_QUIET=true
GRUB_TIMEOUT=15
GRUB_CMDLINE_LINUX_DEFAULT="net.ifnames=0 ipv6.disable=1 video=1440x900@60
noresume 3 "
GRUB_CMDLINE_LINUX=""

# Uncomment to automatically save last booted menu entry in GRUB2 environment

# variable `saved_entry'
# GRUB_SAVEDEFAULT="true"
#Uncomment to enable BadRAM filtering, modify to suit your needs

# This works with Linux (no patch required) and with any kernel that obtains
# the memory map information from GRUB (GNU Mach, kernel of FreeBSD ...)
# GRUB_BADRAM="0x01234567,0xfefefefe,0x89abcdef,0xefefefef"
#Uncomment to disable graphical terminal (grub-pc only)

GRUB_TERMINAL="gfxterm"
# The resolution used on graphical terminal
#note that you can use only modes which your graphic card supports via VBE

# you can see them in real GRUB with the command `vbeinfo'
GRUB_GFXMODE="auto"
# Uncomment if you don't want GRUB to pass "root=UUID=xxx" parameter to Linux
# GRUB_DISABLE_LINUX_UUID=true
#Uncomment to disable generation of recovery mode menu entries

# GRUB_DISABLE_LINUX_RECOVERY="true"
#Uncomment to get a beep at grub start

# GRUB_INIT_TUNE="480 440 1"
SUSE_BTRFS_SNAPSHOT_BOOTING="true"
GRUB_USE_LINUXEFI="true"
GRUB_DISABLE_OS_PROBER="true"
GRUB_ENABLE_CRYPTODISK="n"
GRUB_CMDLINE_XEN_DEFAULT="vga=gfx-1024x768x16"