So what the Suse installer is telling you is that you really should use a /boot partition if installing on a GPT partition table.
Why is it telling ME that when I trusted the partitioning to the installer? I really don't understand how that should be my fault for the partitioner to act faulty. And btw. there's only two options: 1) to erase the disk if needed and 2) erase the entire disk anyway. I selected the second one because the first one didn't even work at all, so from my perspective it should have not used any potential GPT partitions that the previous distro could've potentially created, but erased the entire thing and start from scratch with everything it would need, including a valid boot partition. If OpenSUSE, for some reason, requires me to wipe my drive clean BEFORE I even start the installer, then they should specify that beforehand - or provide a less antique installer that can actually do it itself.