Since I don’t see any new replies I’ll just say something that might work or might not (I’m no expert).
There is a tool named Super Grub2 Disk as for what I knows it can help you boot the system when it’s damaged the grub thing, it once helped me to boot the system but never solved the root of the problem. There is a video about it… https://www.youtube.com/watch?v=7JfU2lFucgQ
Now… just now I updated grub and saw and ran the command that’s posted here:
https://forum.endeavouros.com/t/grub-update-in-the-testing-repo/46285/3
apparently it’s necessary after updating grub.
As I said I’m no expert, but I think that this might probably work: Use the tool to boot the system, apply that command, that of course if grub was updated on that update.
I hope my comment helps you.