Hi Leap and Tumbleweed don’t co-exist without some tweaks with the efi file location directory name, unless you created a separate /boot/efi partition for it?
Look down in /boot/efi/EFI and you may only have one directory with opensuse?
What is the output from;
efibootmgr -v os-prober
But you should be able to add Leap to grub…