I went over this with @abucodonosor and he looked in openSUSE repositories and he found what problem is. openSUSE uses custom syntax for their os-prober and grub2 btrfs patches that are not compatible with OM Lx code. The problem is they literally call btrfs something different (xbtrfs). There is more to openSUSE customization that makes this very difficult for OM devs to fix.
I did test installs of SUSE Leap 15.1 with btrfs and OM Lx will not create boot entry for that. Test install of SUSE Leap 15.1 with ext4 and OM Lx will boot that. Other file system types are unknown unless we get reports from users.
So this is a problem that requires a workaround. Either switch boot loaders in BIOS for the computer as needed. (Or UEFI settings to be technically correct for UEFI computers.) Or use openSUSE bootloader if it recognizes your OM Lx system (and others).
Note: As I long time Linux multi-booter that used openSUSE myself for years I can report that openSUSE was always the most problematic system for me in terms of cooperating with other Linux boot loader configs. I frequently, but not always, had to do the “change boot-loader in BIOS” workaround myself specifically for openSUSE.
Note-2: This may be possible to fix in code but OM developers are few in number and have to prioritize fixing things that affect all users first, most users next. This is an issue that would only affect a few users so it is a priority question. (This statement is “as @ben79 understands things at this time”.)