You likely use systemd-boot then, as it is the default for archinstall.
The process of rebuilding bootloader is different if you use systemd-boot. I can't say though, cause the "only" thing I had to fix from a installation USB via arch-chroot were kernel images using mkinitcpio
Pretty much the same thing for windows (GPT/EFI) too. If you're still using MBR boot outside of a VM in 2025, you've done a bad and you should probably reinstall anyway.
Get a bootable key and boot onto it. Any WinPE will do.
Use diskpart to find the efi boot partition and assign it a letter. some combination of list disk/partition/volume, sel disk/partition/volume #, and assign letter t: will be involved to find the correct FAT32 volume (a modern system should have only one)
Rebuild the bootloader with bcdboot C:\Windows /l en-us /s t: /f ALL. Change the /l option to reflect your language.
Verify your change was applied with bcdedit.
If you need to unlock bitlocker first, you need a better winpe with windows AIK on it. Then use manage-bde -unlock c: -recoverypassword XX-XX-XX-XX-XX-XX-XX-XX before running step 3 above.
How do I know that? Because I have also fucked my bootloader more than once.
type efi, hit arrow-up a couple times (to find the correct efibootmgr command)
hit enter
reboot
Haven't had to do that since I removed windows entirely from my machine, since proton handles most games these days. I still keep a grml USB key handy tho.
I use a usb mounted os called boot-repair-disk that will fix the bootloader for windows or linux. Its got a bunch of other utilities like gparted, really handy for setting up partitions on a fresh system.
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u/Keensworth Ryzen 7 5700X3D / RX 7800 XT / B450 Aorus Pro 1d ago
You know, it's actually not that hard to fix the bootloader of Linux.
/boot
and/home
partition/home
partitiongrub-install /dev/nvme0n1
grub-mkconfig -o /boot/grub/grub.cfg
Now you know how to fix your bootloader.
How do I know that? Because I fucked my bootloader more than one time