I apologize for the semi-driveby comment but hopefully this will help.

I had a boot problem during a laptop fresh install that I kind of understood but just could not solve a couple years back relating to some weirdness with that specific laptop.

I used boot repair. This is surely not the howto I followed, it’s just the first recent one I found. My recollection was that it wasn’t too hard to sniff my way through, I wasn’t at all sure it had worked, but sure enough it came up fine on the very next reboot.

www.debugpoint.com/boot-repair-disk/

100% there are other howtos out there, I have not vetted this one beyond skimming it to see it looked reasonable.