Hi again, @sm-wilson.
You're welcome 
Unfortunately, my personal use cases of dual-boot ("dualboot") / multi-boot ("multiboot") are only for a Windows 10 + Ubuntu MATE 22.04 LTS ("Jammy Jellyfish") dual boot scenario and for a Windows 11 + Ubuntu MATE 22.04 LTS ("Jammy Jellyfish") dual boot scenario. I've never tried to set up a true multi-boot scenario as is the case of your setup (where you have a "triple-boot" / "tripleboot" scenario of openSUSE Tumbleweed + Ubuntu MATE 24.04 LTS ("Noble Numbat") + Windows).
Naturally, I suggest that you first make sure that you have good backups of your files before changing BIOS / UEFI settings and/or Boot Loader configurations, in case that your system becomes unbootable by any change (I imagine that you're already taking your precautions about that).
As you've mentioned that your BIOS / UEFI settings got apparently reset (that is strange!), I guess you may want to try to check if "Fast Boot" got enabled in your BIOS / UEFI settings and disable it, if you find that it got turned on, to see if that helps.
Other than that, my only guess (but it's only a guess!) is that the GRUB setups of openSUSE Tumbleweed and Ubuntu MATE 24.04 may be in conflict with each other, but I may be completely wrong about that.
You may want to try to use something like the "rEFInd Boot Manager" - https://www.rodsbooks.com/refind/ - to see if it helps in your case, but I don't have experience with "rEFInd" to be able to help you more with that. Maybe someone else here in the Ubuntu MATE Community can help you more? I know that, for instance, @watchpocket uses "rEFInd" (see, for instance, the following topic: "In rEFInd, need 2 different OS icons for 2 instances of same OS" - https://ubuntu-mate.community/t/in-refind-need-2-different-os-icons-for-2-instances-of-same-os/24722 )