Well the fact that you don’t understand the issue is part of it. See there are several ways disks can be partitioned and several ways a bios can go about finding kernels to boot on said disks, all of this applies to windows as well btw.
Bios legacy + MBR partitioned with a bootloader written into the first 512 bytes of a disk and the bios being directed to that disk. This is the old way of doing it.
UEFI + GPT partition scheme. Here you have one or more partition marked as bios+uefi, formatted in fat32, that the bios will comb for boot entries. It’s the modern way of doing this.
What you have is probably a mix of the two. It’s likely that one of your linux installs partitioned your disk as GPT while your your system still boots in bios legacy. The installer is now getting mixed signals, one one hand the bios is detected as legacy mode, on the other it’s looking at a GPT partition table. Now technically you probably could write the bootloader just like in option 1., but if you ever change your bios to uefi mode, which is required for modern operating systems like windows you would end up with an non bootable system. And not just in a “oopsie, I need to boot a rescue disk and fix this”-kind of way but a “we need to nuke the entire partition table and start over”-kind of way.
So what the Suse installer is telling you is that you really should use a /boot partition if installing on a GPT partition table.
Btw if you check the correct option at install time(the one about using the entire harddrive) it should automatically create a MBR partitioned disk for you which avoids this issue as it’s not a ungodly mix of 1. and 2.
This error isn’t a bug, it’s a feature pointing out a serious problem with your machines setup(the one below the OS level). Yes you can probably ignore it, as other distros might or might not, but it’s generally not a good idea. SuSE has a couple of these hang ups since it has an enterprise background and takes some things more serious than other distros. For example having closed ports for printers in the active on default firewall being one stellar example of this. It cause no end of issues for people struggling to setup their printers, that being said it is a security issue and opensuse decided it wasn’t going to sacrifice security of every system because some people want to use a printer.