Lesson I also learned when I started out with Linux… don’t fuck with grub unless you really understand what you’re doing! Borking grub is a right of passage imo.
I’m not sure how to fix your issue (I gave up on dual booting and just have windows in a virtual machine, so Windows doesn’t mess up grub).
I always keep backups of the working grub config in case I need to restore. Just boot into a version of Linux on a usb key and copy the working config.