It is frustrating to answer questions that are full from technical knowledge unawareness, but, for the sake of future readers, I will answer once more and not close the topic (since you imply of there is a fault in Garuda system without any proof at all, which is , at least, rude).
This means Garuda is a Normal Linux distro, using grub, in a mixed UEFI/MSdosLegacy system.
There is NO problem. It’s a YOUR desire issue and misconception, no offense (again).
Have you read any instructions of the proper method and possible implications? Can you post even one link to what you have been advised to do?
I hope you have one, because if you don’t, it is weird (gently speaking) that you so strongly insist about technical issues.
How were you booting prior and after mobo replacement?
If you don’t know what I mean:
- Were you using BIOS boot menu?
- Were you using Windows boot loader? OK, I’m joking. There is no multiboot feature for Windows.
- Were you using Manjaro
gruband in what boot mode, after all?
I will not answer further, unless some sane response comes out and some respect is shown. Each user is the System Administrator of his system, whether knowingly or not.