I have two partitions on my SSD, one with Leap and the other with Tumbleweed.
When I start the Leap partition, I can select the Tumbleweed installation in Grub.
However, it doesn’t start with the message:
error: …/…/grub-core/kern/efi/sb.c:192:bad shim signature. error: …/…/grub-core/loader/i386/efi/linux.c:168:you need to load the kernel first.
Press any key to continue…
The same thing happens in reverse.
Within both partitions, I selected “probe foreign OS” in yast->‘boot loader’->‘bootloader options’ as well as “secure boot support” in ‘boot code options’.
How can I start Tumbleweed from Leap Grub?
Selecting it via the BIOS boot menu is very cumbersome (time-critical).
I have enrolled the Tumbleweed shim certificate while running Leap, and I have enrolled the Leap shim certificate while booted to Tumbleweed (from BIOS boot manager). After doing that, I have no trouble booting either Leap or Tumbleweed from either boot menu.
On my current desktop computer, I did that with Leap 15.5 (the first system that I installed). I have no needed to redo it.
If the release manager changes to a newer CA certificate, then you will need to redo it.
The certificate is actually in “shim” itself. And there’s a copy in "/etc/uefi/certs. The EFI entry used is what decides which version lf “shim”. Tumbleweed uses the openSUSE CA certificate, while Leap uses the SUSE CA certificate.